Techniques for designing and manufacturing precision-folded, high strength, fatigue-resistant structures and sheet therefor

ABSTRACT

A process for designing and manufacturing precision-folded, high strength, fatigue-resistant structures and a sheet therefore. The techniques include methods for precision bending of a sheet of material ( 41, 241, 341, 441, 541 ) along a bend line ( 45, 245, 345, 445,543 ) and a sheet of material formed with bending strap-defining structures, such as slits or grooves ( 43, 243, 343, 443, 542 ), are disclosed. Methods include steps of designing and then separately forming longitudinally extending slits or grooves ( 43, 243, 343, 443, 542 ) through the sheet of material in axially spaced relation to produce precise bending of the sheet ( 41, 241, 341, 441,541 ) when bent along the bend line ( 45, 245, 345, 445, 543 ). The bending straps have a configuration and orientation which increases their strength and fatigue resistance, and most preferably slits or arcs are used which causes edges ( 257, 457 ) to be engaged and supported on faces ( 255, 455 ) of the sheet material on opposite sides of the slits or arcs. The edge-to-face contact produces bending along a virtual fulcrum position in superimposed relation to the bend line ( 45, 245, 345, 445, 543 ). Several slit embodiments ( 43, 243, 343, 443, 542 ) suitable for producing edge-to-face engagement support and precise bending are disclosed, as is the use of the slit sheets to produce various three-dimensional structures and to enhance various design and fabrication techniques.

RELATED APPLICATIONS

[0001] This application is a Continuation-in-Part Application based upona co-pending patent application Ser. No. 10/256,870, filed Sep. 26,2002, and entitled METHOD FOR PRECISION BENDING OF SHEET OF MATERIALS,SLIT SHEETS FABRICATION PROCESS, which was a Continuation-in-PartApplication based upon a co-pending parent application Ser. No.09/640,267, filed Aug. 17, 2000, and entitled METHOD FOR PRECISIONBENDING OF A SHEET OF MATERIAL AND SLIT SHEET THEREFOR, now U.S. Pat.No. 6,481,259 B1.

TECHNICAL FIELD

[0002] The present invention relates, in general, to the designing andprecision folding of sheets of material and the manufacture ofstructures therefrom. More particularly, the present invention relatesto processes of designing, preparing and manufacturing, including, butnot limited to, ways of preparing sheet material, in order to enableprecision folding and to the use of such processes for rapidtwo-dimension- to- three-dimensional folding of high strength,fatigue-resistant structures or assemblies.

BACKGROUND ART

[0003] A commonly encountered problem in connection with bending sheetmaterial is that the locations of the bends are difficult to controlbecause of bending tolerance variations and the accumulation oftolerance errors. For example, in the formation of the housings forelectronic equipment, sheet metal is bent along a first bend line withincertain tolerances. The second bend, however, often is positioned basedupon the first bend, and accordingly, the tolerance errors canaccumulate. Since there can be three or more bends which are involved tocreate the chassis or enclosure for the electronic components, theeffect of cumulative tolerance errors in bending can be significant.Moreover, the tolerances that are achievable will vary widely dependingon the bending equipment, and its tooling, as well as the skill of theoperator.

[0004] One approach to this problem has been to try to control thelocation of bends in sheet material through the use of slitting orgrooving. Slits and grooves can be formed in sheet stock very precisely,for example, by the use of computer numerically controlled (CNC) deviceswhich control a slit or groove forming apparatus, such as a laser, waterjet, punch press, knife or other tool.

[0005] Referring to FIG. 1, a sheet of material 21 is shown which has aplurality of slits or grooves 23 aligned in end-to-end, spaced apartrelation along a proposed bend line 25. Between pairs of longitudinallyadjacent slits or grooves are bending webs, splines or straps 27 whichwill be plastically deformed upon bending of sheet 21. Webs 27 hold thesheet together as a single member. When grooves that do not penetratethrough sheet 21 are employed, the sheet of material is also heldtogether by the web of material behind each groove.

[0006] The location of grooves or slits 23 in sheet 21 can be preciselycontrolled so as to position the grooves or slits on bend line 25 withinrelatively close tolerances. Accordingly, when sheet 21 is bent afterthe grooving or slitting process, the bend occurs at a position that isvery close to bend line 25. Since slits can be laid out on a flat sheetof material precisely, the cumulative error is much less in such abending process, as compared to one in which bends are formed by a pressbrake, with each subsequent bend being positioned by reference to thepreceding bend.

[0007] Nevertheless, even a grooving-based or slitting-based bending ofsheet material has its problems. First, the stresses in bending webs orstraps 27, as a result of plastic deformation of the webs and slittingat both ends of webs 27, are substantial and concentrated. For grooving,the stresses on the material behind or on the back side of the groovealso are substantial and very concentrated. Thus, failures at webs 27and/or behind grooves 23 can occur. Moreover, the grooves or slits donot necessarily produce bending of webs 27 directly along bend line 25,and the grooving process is slow and inconsistent, particularly whenmilling or point cutting V-shaped grooves. Grooving, therefore, is notin widespread commercial use.

[0008] As can be seen in FIGS. 1A and 1B, if sheet 21 is slit, as isshown at 23 a and/or grooved, as shown at 23 b, and then bent, bendingwebs 27 a and 27 b will experience plastic deformation and residualstress. For slit 23 a, of course, material will be completely removed orsevered along the length of the slit. For V-shaped groove 23 b, therewill be a thin web 29 between groove 23 b and the convex outside of thebend, but it also will be plastically deformed and highly stressed. Thebend for V-shaped grooving will normally be in a direction closinggroove 23 b so that the side faces come together, as shown in FIG. 1B.Loading of the bent structure of FIGS. 1A and 1B with a vertical forceF_(V) and/or a horizontal force F_(H) will place the bend, with theweakening slits and/or grooves and the plastically deformed straps orwebs 27 a, 27 b, as well as thin web 29, under considerable stress.Failure of the structure will occur at lower force levels than if anon-slitting or non-grooving bending process was used.

[0009] Another scheme for sheet slitting to facilitate bending has beenemployed in the prior art. The slitting technique employed to producebends, however, was designed primarily to produce visual or decorativeeffects for a sculptural application. The visual result has beendescribed as “stitching,” and the bends themselves have beenstructurally reinforced by beams. This stitched sculpture was exhibitedat the New York Museum of Modern Art by at least 1998, and the sheetslitting technique is described in Published United States PatentApplication U.S. 2002/0184936 A1, published on Dec. 12, 2002, (the“Gitlin, et al Application.”). The sculpture is also shown and describedin the publication entitled “Office dA” by Contemporary WorldArchitects, pp. 15, 20-35, 2000.

[0010]FIGS. 2, 2A and 2B of the present drawing show one example of thestitching technique employed.

[0011] One embodiment of the Office dA or Gitlin, et al. Application isshown in FIG. 2. A plurality of slits 31 is formed in a sheet material32. Slits 31 are linear and offset laterally of each other alongopposite sides of a bend line 33. The slits can be seen tolongitudinally overlap so as to define what will become bending splines,webs, straps or “stitches” 34 between the overlapped slit ends. FIGS. 2Aand 2B show an enlarged side elevation view of one end of one slit insheet 32, which has been bent along bend line 33 by 90 degrees, andsheet portions 35 and 36 on opposite sides of the bend line areinterconnected by the twisted straps or “stitches” 34, which twist orstitch between the 90 degree sheet portions 35,36. The architects of theNew York Museum of Modern Art sculpture recognized that the resultingbend is not structurally very strong, and they have incorporatedpartially hidden beams welded into the sculpture in the inner verticesof each of the stitched bends.

[0012] Since slits 31 are parallel to bend line 33, straps 34, whichalso have a constant or uniform width dimension, are twisted orplastically deformed in torsion over their length, with the result thatat the end of a 90° bend a back side of the strap engages face 38 on theother side of slit 31 at position 37. Such engagement lifts sheetportion 35 up away from face 38 on sheet portion 36, as well as tryingto open end 40 of the slit and producing further stress at the slit end.The result of the twisting of straps 34 and the lifting at the end ofthe bend is a gap, G, over the length of slit 31 between sheet portion35 and face 38. Twisted straps or stitches 34 force sheet portion 35 offof face 38 and stress both slit ends 40 (only one slit end 40 is shownbut the same stress would occur at the other slit end 40 of the slip 31shown in FIGS. 2A and 2B).

[0013] Gaps G are produced at each slit 31 along the length of bend line33 on alternative sides of the bend line. Thus, at each slit a sheetportion is forced away from contact with a slit-defining face instead ofbeing pulled into contact with, and thus full support by, the face.

[0014] Moreover, and very importantly, the slitting configuration ofFIG. 2 stresses each of straps 34 to a very high degree. As the straplength is increased (the length of overlap between the ends of slits 31)to attempt to reduce the stress from twisting along the strap length,the force trying to resiliently pull or clamp a sheet portion against anopposing face reduces. Conversely, as strap length 34 is decreased,twisting forms micro tears in the constant width straps with resultantstress risers, and the general condition of the twisted straps is thatthey are overstressed. This tends to compromise the strength of the bendand leaves a non-load bearing bend.

[0015] A vertical force (Fv in FIG. 2B) applied to sheet portion 35 willimmediately load twisted and stressed strap 34, and because there is agap G the strap will plastically deform further under loading and canfail or tear before the sheet portion 35 is displaced down to engagementwith and support on face 38. A horizontal force FH similarly will tendto crush the longitudinally adjacent strap 34 (and shear strap 34 inFIG. 2B) before gap G is closed and the sheet portion 35 is supported onthe opposing slit face 38.

[0016] Another problem inherent in the slitting scheme of FIGS. 2-2B andthe Gitlin, et al. Application is that the constant strap width cannotbe varied independently of the distance between slits, and the strapwidth cannot be less than the material thickness without stressing thestraps to the extreme. When slits 31 are parallel to each other andlongitudinally overlapping, the strap width, by definition, must equalthe spacing or jog between slits. This limits the flexibility indesigning the bends for structural loading of the straps. Still further,the slits terminate with every other slit end being aligned and directedtoward the other. There is no attempt, therefore, to reduce stressrisers and micro-crack propagation from occurring at the ends of theslits, and aligned slit ends can crack under loading.

[0017] The sheet slitting configuration of FIGS. 2-2B, therefore, can bereadily employed for decorative bends, but it is not optimally suitedfor bends which must provide significant structural support and fatigueresistance.

[0018] The Gitlin et al. Application also teaches the formation ofcurved slits (in FIGS. 10a, 10 b), but the slits again parallel a curvedbend line so that the width of the bending straps is constant, thestraps extend along and parallel to the bend line, not across it, thestraps are twisted in the extreme, the slit ends tend to directmicro-cracks and stress concentrations to the next slit, and theapplication teaches employing a slit kerf which results in engagement ofthe opposite side of the slit, at 37, only at the end of the bend.

[0019] A simple linear perforation technique also was used by the samearchitects in an installation of bent metal ceiling panels in a pizzarestaurant in Boston. Again, the bent sheet components by linearperforation were not designed to bear significant unsupported loadsalong the bends.

[0020] Slits, grooves, perforations, dimples and score lines also havebeen used in various patented systems as a basis for bending sheetmaterial. U.S. Pat. No. 5,225,799 to West et al., for example, uses agrooving-based technique to fold up a sheet of material to form amicrowave wave guide or filter. In U.S. Pat. No. 4,628,161 to St. Louis,score lines and dimples are used to fold metal sheets. In U.S. Pat. No.6,210,037 to Brandon, slots and perforations are used to bend plastics.The bending of corrugated cardboard using slits or die cuts is shown inU.S. Pat. No. 6,132,349 and PCT Publication WO 97/24221 to Yokoyama, andU.S. Pat. Nos. 3,756,499 to Grebel et al. and 3,258,380 to Fischer, etal. Bending of paperboard sheets also has been facilitated by slitting,as is shown in U.S. Pat. Nos. 5,692,672 to Hunt, 3,963,170 to Wood and975,121 to Carter. Published U.S. Patent Application No. US 2001/0010167A1 also discloses a metal bending technique involving openings, notchesand the like and the use of great force to produce controlled plasticflow and reduced cracking and wrinkling.

[0021] In most of these prior art bending systems, however, the bendforming technique greatly weakens the resulting structure, or precisionbends are not capable of being formed, or bending occurs by crushing thematerial on one side of the bend. Moreover, when slitting is used inthese prior art systems, in addition to structural weakening and thepromotion of future points of structural failure, the slitting can makethe process of sealing a bent structure expensive and difficult. Theseprior art methods, therefore, are less suitable for fabricatingstructures that are capable of containing a fluid or flowable material.

[0022] The problems of precision bending and retention of strength aremuch more substantial when bending metal sheets, and particularly sheetsof substantial thickness. In many applications it is highly desirable tobe able to bend metal sheets with low force, for example, by hand withonly hand tools, or with only moderately powered tools. Such bending ofthick metal sheets, of course, poses greater problems.

[0023] In another aspect of the present invention the ability toovercome prior art deficiencies in slitting-based bending of sheetmaterial is applied to eliminate deficiencies in prior art metalfabrication techniques and the structures resulting therefrom.

[0024] A well known prior art technique for producing rigid threedimensional structures is the process of cutting and joining togetherparts from sheet and non-sheet material. Jigging and welding, clampingand adhesive bonding, or machining and using fasteners to join togetherseveral discrete parts has previously been extensively used to fabricaterigid three-dimensional structures. In the case of welding, for example,a problem arises in the accurate cutting and jigging of the individualpieces; the labor and machinery required to manipulate a large number ofparts, as well as the quality control and certification of multipleparts. Additionally, welding has the inherent problem of dimensionalshape warping caused by the heat-affected zone of the weld.

[0025] Traditional welding of metals with significant material thicknessis usually achieved by using parts having beveled edges often made bygrinding or single point tools, which add significantly to thefabrication time and cost. Moreover, the fatigue failure ofheat-affected metals is unpredictable for joints whose load-bearinggeometries rely entirely on welded, brazed or soldered materials.Fatigue failure of welds usually is compensated for by increasing themass of the components, which are welded together and the number anddepth of the welds. The attendant disadvantage of such over design is,of course, excessive weight.

[0026] With respect to adhesively bonding sheet and non-sheet materialalong the edges and faces of discrete components, a problem arises fromthe handling and accurate positioning the several parts and holding orclamping them in place until the bonding method is complete.

[0027] Another class of prior art techniques related to the fabricationof three-dimensional structures are the Rapid Prototyping methods. Theseinclude stereo lithography and a host of other processes in which adesign is produced using a CAD system and the data representation of thestructure is used to drive equipment in the addition or subtraction ofmaterial until the structure is complete. Prior art Rapid Prototypingtechniques are usually either additive or subtractive.

[0028] The problems associated with subtractive Rapid Prototypingmethods are that they are wasteful of materials in that a block ofmaterial capable of containing the entire part is used and then arelatively expensive high-speed machining center is required toaccurately mill and cut the part by removal of the unwanted material.

[0029] Problems also exist with prior art additive Rapid Prototypingtechniques. Specifically, most such techniques are optimized for a verynarrow range of materials. Additionally, most require a specializedfabrication device that dispenses material in correspondence with thedata representing the part. The additive Rapid Prototyping processes areslow, very limited in the scale of the part envelope and usually do notmake use of structurally robust materials.

[0030] Generally in the prior art, therefore, sheet slitting or groovingto enable sheet bending has produced bends, which lack the precision andstrength necessary for commercial structural applications. Thus, suchprior art sheet bending techniques have been largely relegated to lightgauge metal bending or decorative applications, such as sculpture.

[0031] In a broad aspect of the present invention, therefore, it is animportant object of the present invention to be able to bend sheetmaterial in a very precise manner and yet produce a bend, which iscapable of supporting substantial loading and is resistant to fatiguefailures.

[0032] Another object of this aspect of the present invention is toprovide a method for precision bending of sheets of material usingimproved slitting techniques, which enhance the precision of thelocation of the bends, the strength of the resulting structures andreduce stress-induced failures.

[0033] Another object of the present invention is to provide a precisionsheet bending process and a sheet of material which has been slit orgrooved for bending and which can be used to accommodate bending ofsheets of various thicknesses and of various types of non-crushablematerials.

[0034] Another object of the present invention is to provide a methodfor slitting sheets for subsequent bending that can be accomplishedusing only hand tools or power tools which facilitate bending but do notattempt to control the location of the bend.

[0035] Another object of the present invention is to be able to bendsheet material into high strength, three-dimensional structures havingprecise dimension tolerances.

[0036] It is another object of the present invention to be able to bendsheet materials into precise three-dimensional structures that areeasily and inexpensively sealed thus enabling the containment of fluidor flowable materials.

[0037] In a broad aspect of the present invention relating to the use ofslit-based bending to enhance fabrication and assembly techniques, it isan object of the present invention to provide a new Rapid Prototypingand Advanced Rapid Manufacturing technique that employs a wide range ofmaterials including many that are structurally robust, does not employspecialized equipment other than what would be found in any modernfabrication facility, and can be scaled up or down to the limits of thecutting process used.

[0038] It is another object of this aspect of the present invention toprovide features within the sheet of material to be bent that assist inthe accurate additive alignment of components prior to and after thesheet material is bent.

[0039] A further object of the present invention is to provide afabrication method that serves as a near-net-shape structural scaffoldfor multiple components arranged in 3D space in the correct relationshipto each other as defined by the original CAD design process.

[0040] It is a further object of the present invention to provide amethod of fabricating welded structures that employs a smaller number ofseparate parts and whose edges are self jigging along the length of thebends and whose non-bent edges provide features that facilitate jiggingand clamping in preparation for welding. In this context it is yetanother object of the present invention to provide a superior method ofjigging sheet materials for welding that dramatically reduces warpingand dimensional inaccuracy caused by the welding process.

[0041] Yet another object of the present invention is to provide a novelwelded joint that provides substantial load-bearing properties that donot rely on the heat affected zone in all degrees of freedom and therebyimprove both the loading strength and cyclical, fatigue strength of theresulting three dimensional structure.

[0042] Still another object of the present invention is to provide asuperior method for:

[0043] 1) reducing the number of discrete parts required to fabricate astrong, rigid, dimensionally accurate three dimensional structure, and

[0044] 2) inherently providing a positioning and clamping method for thevarious sides of the desired three dimensional structure that can beaccomplished through the bent and unbent edges of the present inventionresulting in a lower cost, higher yield fabrication method.

[0045] It is a further object of the present invention to provide amethod of fabricating a wide variety of fluid containing casting moldsfor metals, polymers, ceramics and composites in which the mold isformed from a slit, bent, sheet of material which can be either removedafter the solidification process or left in place as a structural orsurface component of the finished object.

[0046] Still another object of the present invention is to provide asheet bending method that is adaptable for use with existing slittingdevices, enables sheet stock to be shipped in a flat or coiled conditionand precision bent at a remote location without the use of a pressbrake, and enhances the assembly or mounting of components within and onthe surfaces in the interior of enclosures formed by bending of thesheet stock after component affixation to the sheet stock.

[0047] Still another object of the present invention is to provide aprecision folding technique that can be used to create accurate,precise, load-bearing folds in sheets of material, including but notlimited to, metals, plastics, and composites.

[0048] Another object of the present invention is to provide a precisionfolding technique that allows folding around a virtual bend line andrequires considerably less force to accomplish the fold thanconventional bending techniques.

[0049] Another object of the present invention is to provide a precisionfolding technique that is essentially linearly scalable independently ofthe thickness or microstructural characteristics of the material

[0050] Another object of the present invention is to form the geometriesdescribed herein whether by a slitting/removal process, a severingprocess or by an additive process, and arrive at the advantages hereindescribed by any route.

[0051] Yet another object of the present invention is to provide aprecision folding technique for folding a non-crushable material inwhich the microstructure of the material remains substantially unchangedaround the fold.

[0052] The methods and discrete techniques for designing and precisionfolding of sheet material, the fabrication techniques therefor, and thestructures formed from such precision bending of the present inventionhave other features and objects of advantage which will become apparentfrom, or are set forth in more detail in, the accompanying drawing andthe following description of the Best Mode of Carrying Out TheInvention.

DISCLOSURE OF INVENTION

[0053] In a broad aspect the present invention, bending strap-definingstructures, which are preferably slits but may be grooves, are used toconfigure bending straps in the sheet of material that cause the bentsheet to have improved precision in the bend location and substantiallyimproved bend strength.

[0054] Briefly, in a preferred embodiment a sheet of material is formedwith a plurality of slits that are positioned relative to a proposedbend line and configured to allow bending of the sheet of materialprecisely along the bend line as a result of edge-to-face engagement ofmaterial on opposite sides of the slits during bending for increasedbend strength and dimensional accuracy.

[0055] Most preferably the longitudinally adjacent slits are equallytransversely spaced on opposite sides of the bend line to define bendingstraps that extend obliquely across the bend line. The slits arepreferably arcuate with convex side facing or closest to the bend lineso that the width dimension of the straps increases in both directionsfrom a midpoint, or a constant width region, of the straps. The slitsalso preferably include crack propagation resisting end portions tofurther reduce the likelihood of stress failures.

[0056] The method for precision bending of a sheet of material of thepresent invention is comprised, briefly, of the steps of forming aplurality of longitudinally extending slits through the sheet in axiallyspaced relation in a direction extending along, and proximate to, a bendline to define bending straps or webs between adjacent ends of pairs ofthe slits. The slits are further configured and positioned during theforming step to produce edge-to-face engagement of the sheet material onopposite sides of the slits during bending of the sheet of material. Themethod also can include the step of bending the sheet of material alongthe bend line to produce such precision-enhancing edge-to-faceengagement of the material on opposite sides of the slits throughout thebend.

[0057] In one embodiment, the slitting step is accomplished by formingtwo elongated slits longitudinally shifted along the bend line, witheach slit having a slit end portion which diverges away from the bendline to provide a pair of adjacent slit portions on opposite sides ofthe bend line which define an oblique bending strap extending across thebend line with increasing width in both directions from the bend line.The slit kerf and jog distance between opposing rows of arcuate slitsare dimensioned and positioned to produce interengagement of an edge ofthe sheet of material on one side of the slits with a face of the sheetof material on the opposite side of the slits during bending. Mostpreferably the slits are arcuate and produce continuous and progressiveengagement of an edge with an opposing face, with the result that theedge is resiliently clamped and held against the opposing face over asubstantial portion of the length of the slit during bending for controlof the bending precision and enhancement of the strength of the bentsheet.

[0058] In another embodiment of the method of the present invention, thestep of slitting is accomplished by forming a first elongated slitthrough the sheet of material along the bend line, which slit iscomposed of a pair of proximate, transversely spaced apart, parallel andlongitudinally extending, first slit segments connected near a commontransverse plane by a transversely extending slit segment; and byforming a second elongated slit in substantially longitudinally alignedand longitudinally spaced relation to the first elongated slit. The stepof forming the second elongated slit also preferably is accomplished byforming a pair of proximate, transversely spaced apart, parallel andlongitudinally extending, slit segments connected near a commontransverse plane by a transversely extending slit segment. Thus, insteadof one continuous elongated slit, each slit in the pair of slits isformed as a slightly stepped slit proximate a midpoint of the combinedlength of the slit segments.

[0059] In these embodiments, a virtual fulcrum is provided upon bendingthat can be positioned precisely on the bend line to cause bending ofthe bending straps or webs more precisely along the bend line. Thedetailed concept of the virtual fulcrum is described below in the BestMode Of Carrying Out The Invention. The slits may be provided withenlarged end openings, or may curve back on themselves so as to reducestress concentrations proximate the bending webs and resist micro-crackpropagation.

[0060] In another embodiment a single slit is provided with bendingstraps that are configured to pull the sheet on the far side of the bendline toward the slit to maintain edge-to-face engagement during bending.Obliquely oriented bending straps having central axes which converge ona side of the bend line opposite to the side on which the slit ispositioned will produce such edge-to-face contact. Sheet edges can becombined with arcuate slit end portions to define such oblique straps.

DESCRIPTION OF THE DRAWING

[0061]FIG. 1 is a fragmentary, top plan view of a sheet of materialhaving slits and grooves formed therein in accordance with one prior arttechnique.

[0062]FIG. 1A is an enlarged, fragmentary view, in cross section, takensubstantially along the plane of line 1A-1A in FIG. 1, of the sheet ofFIG. 1 when in a bent condition.

[0063]FIG. 1B is an enlarged, fragmentary view, in cross section, takensubstantially along the plane of line 1B-1B of FIG. 1, of the sheet ofFIG. 1 when in a bent condition.

[0064]FIG. 2 is a fragmentary, top plan view of a sheet of materialhaving a plurality of slits formed therein using an alternativeconfiguration known in the prior art.

[0065]FIG. 2A is an enlarged fragmentary side elevation view of thesheet of FIG. 2 bend by about 90 degrees.

[0066]FIG. 2B is a cross sectional view taken substantially along theplane of line 2B-2B in FIG. 2A.

[0067]FIG. 3 is a fragmentary, top plan view of a sheet of material slitin accordance with one embodiment of the present invention.

[0068] FIGS. 4A-4D are fragmentary, top plan views of a sheet ofmaterial which has been slit according to the embodiment of FIG. 3 andwhich is in the process of being bent from a flat plane in FIG. 4A to a90 degrees bend in FIG. 4D.

[0069] FIGS. 5A-5A . . . are fragmentary, cross sectional views, takensubstantially along the planes of lines 5A-5A . . . , in FIGS. 4A-4Dduring bending of the sheet of material.

[0070]FIG. 6 is a top plan view of a sheet of material slit inaccordance with a second embodiment of the present invention.

[0071]FIG. 7 is a top plan view of the sheet of FIG. 6 after being bentby about 90 degrees.

[0072]FIG. 8 is an end view of the sheet of material of FIG. 7.

[0073]FIG. 8A is an enlarged, end elevation view, in cross section, ofthe sheet of material of FIG. 7 taken substantially along the plane of8A-8A in FIG. 7 and rotated by about 45 degrees from FIG. 8.

[0074]FIG. 8B is an enlarged, end elevation view, in cross section, ofthe sheet of material of FIG. 7 taken substantially along the plane of8B-8B in FIG. 7 and rotated by about 45 degrees from FIG. 8.

[0075]FIG. 9 is a fragmentary top plan view of a sheet of material slitaccording to a further alternative embodiment of the present invention.

[0076]FIG. 10 is a side elevation view of the sheet of FIG. 9 afterbending by about 90 degrees.

[0077]FIG. 10A is a fragmentary cross sectional view taken substantiallyalong the plane of line 10A-10A in FIG. 10.

[0078]FIG. 11 is a fragmentary, top plan view of a schematicrepresentation of a further alternative embodiment of a sheet ofmaterial having strap-defining structures constructed in accordance withthe present invention.

[0079]FIG. 11A is a fragmentary top plan view of a slit of theconfiguration shown in FIG. 11 which has been formed using a rapidpiercing laser cutting technique.

[0080]FIG. 12 is a fragmentary, top plan view of one sheet of materialbefore bending and assembly into a curved box beam.

[0081]FIG. 13 is a side elevation view of a curved box beam constructedfrom two sheets of material each being slit as shown in FIG. 12.

[0082]FIG. 14 is an end elevation view of the beam of FIG. 13.

[0083]FIG. 15 is a top plan view of a sheet of material formed withstrap-defining structures and configured for enclosing a cylindricalmember.

[0084]FIG. 16 is a top perspective view of the sheet of material of FIG.15 as bent along bend lines and mounted to enclose a cylindrical member.

[0085]FIG. 17 is a top perspective, exploded view of a corrugatedassembly formed using a sheet of material formed in accordance with thepresent invention.

[0086]FIG. 18 is a top perspective, exploded view of an alternativeembodiment of a sheet of material formed in accordance with the presentinvention.

[0087]FIG. 19 is a top plan view of the slit sheet used to construct analternative embodiment of a corrugated deck prior to bending or folding.

[0088]FIG. 20 is a top perspective view of a corrugated sheet or deckconstructed using the slit sheet material of FIG. 19.

[0089]FIG. 21 is an enlarged, fragmentary perspective view substantiallybounded by line 21-21 in FIG. 20.

[0090]FIG. 21A is an enlarged, fragmentary, top plan view substantiallybounded by line 21A-21A in FIG. 19.

[0091]FIG. 22 is a schematic, end elevation view of a cylindrical memberconstructed using a corrugated sheet similar to that of FIGS. 19 and 20,scaled to define a cylindrical form.

[0092]FIG. 23 is an enlarged, fragmentary, side elevation view of asheet of material slit in accordance with the present invention andhaving a tongue or tab displaced to ensure predictable bending.

[0093]FIG. 23A is a reduced, end elevation view of the sheet of FIG. 23during bending.

[0094]FIG. 24 is a fragmentary, end elevation view of a sheet ofmaterial slit at an oblique angle to the plane of the sheet and shownduring bending a to a complimentary angle.

[0095]FIG. 25 is a side elevation, schematic representation of areel-to-reel sheet slitting line arranged in accordance with the presentinvention.

[0096]FIG. 26 is a top perspective view of a coiled sheet of materialwhich has been slit, for example, using the apparatus of FIG. 25 and isin the process of being rolled out and bent into a three-dimensionalstructure.

[0097] FIGS. 27A-27G are top perspective views of a sheet of materialconstructed in accordance with the present invention as it is being bentinto a cross-braced box beam.

[0098] FIGS. 28A-28E are top perspective views of a sheet of materialconstructed in accordance with the present invention as it is being bentinto a chassis for support of components such as electrical components.

[0099]FIG. 29 is a top perspective, schematic representation of oneembodiment of equipment suitable for low-force bending or folding of theslit sheet of the present invention.

[0100]FIG. 30 is a top perspective, schematic representation of anotherembodiment of sheet bending or folding process of the present invention.

[0101]FIG. 31 is a flow diagram of one aspect of the interactive design,fabrication and assembly processes for slit sheet material bending ofthe present invention.

[0102] FIGS. 32A-32E are top perspective views of a sheet of materialconstructed in accordance with the present invention as it is being bentinto a stud wall/ladder.

[0103]FIG. 33 is a top perspective view of a curved corrugated deck orpanel constructed in accordance with the present invention.

[0104] FIGS. 34A-34E are top perspective views of a sheet of materialincluding swing-out bracing and shown as it is being bent into aswing-out braced box-beam.

[0105]FIG. 35 is a top plan view of a sheet of material slit inaccordance with the present invention and including a single slitembodiment FIG. 36 is a top perspective view of the sheet of FIG. 35 asbent into a roller housing.

[0106]FIG. 37 is a fragmentary top plan view of a sheet of materialhaving differing bend line termination slit configurations.

BEST MODE OF CARRYING OUT THE INVENTION

[0107] Reference will now be made in detail to the preferred embodimentsof the invention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction with thepreferred embodiments, it will be understood that they are not intendedto limit the invention to those embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents, which may be included within the spirit and scope of theinvention as defined by the appended claims.

[0108] The present method and apparatus for precision bending of sheetmaterial is based upon the slitting geometries disclosed in priorapplication Ser. No. 09/640,267, filed Aug. 17, 2000, and entitledMETHOD FOR PRECISION BENDING OF A SHEET OF MATERIAL AND SLIT SHEETTHEREFOR, and Ser. No. 10/256,870, filed Sep. 26, 2002 and entitledMETHOD FOR PRECISION BENDING OF SHEET OF MATERIALS, SLIT SHEETS ANDFABRICATION PROCESS, which are incorporated herein by reference in theirentirety.

[0109] One embodiment of the precision and high strength bending processand apparatus of the present invention can be described by reference toFIGS. 3-5. In FIG. 3 a sheet of material 41 is formed with a pluralityof bending strap-defining structures, in this case slits, generallydesignated 43, along a bend line 45. Slits 43, therefore, arelongitudinally extending and in end-to-end spaced relation so as todefine bending webs or straps 47 between pairs of slits 43. In FIG. 3,slits 43 are provided with stress reducing structures at ends thereof,namely openings 49, so as to effect a reduction in the stressconcentration in bending webs 47. It will be understood from thedescription below, however, that stress reducing structures, such asenlarged openings 49 in FIG. 3, are not required for realization of thebenefits of the precision bending system of the present invention.

[0110] For the embodiment of slits 43 shown in FIG. 3, however, eachlongitudinally extending slit between the slit ends is laterally ortransversely stepped relative to bend lines 45. Thus, a slit, such asslit 43 a, is formed with a pair of longitudinally extending slitsegments 51 and 52 which are positioned proximate to, and preferablyequidistant on opposite sides of, and substantially parallel to, bendline 45. Longitudinal slit segments 51 and 52 are further connected by atransversely extending slit segment 53 so that slit 43 a extends fromenlarged opening 49 a to enlarged opening 49 b along an interconnectedpath which opens to both of the enlarged openings and includes bothlongitudinally extending slit segments 51, 52 and transverse slitsegment 53.

[0111] The function and advantages of such stepped slits can best beunderstood by reference to FIGS. 4A-4D, and the corresponding FIGS.5A-5C to 5A . . . -5C . . . , wherein the bending or folding of a sheetof material 41, such as shown in FIG. 3 is illustrated at variousstages. In FIG. 4A, sheet 41 is essentially slit as shown in FIG. 3.There is a difference between FIGS. 3 and 4A in that in FIG. 3 a kerfwidth or section of removed material is shown, while in FIG. 4A the slitis shown without any kerf, as would be produced by a slitting knife orpunch. The effect during bending, however, is essentially the same ifthe kerf width is small enough that the material on the opposite sidesof the slit interengage during bending. The same reference numerals willbe employed in FIGS. 4A-5C . . . as were employed in FIG. 3.

[0112] Thus, sheet 41 is shown in a flat condition before bending inFIG. 4A. Longitudinally extending slit-segments 51 and 52 are shown inFIG. 4A and in the cross sections of FIGS. 5A-5C. The positions of thevarious cross sections of the sheet are also shown in FIG. 4A.

[0113] In FIG. 4B, the sheet has been bent slightly along bend line 45,which can best be seen in FIGS. 5A.-5C. As can be seen in FIGS. 5A. and5B., slits 51 and 52 have opened up along their top edges and theportion of the sheet which extends beyond bend line 45 was referred toin U.S. Pat. No. 6,481,259 B1 and U.S. Application Serial No. 10/256,870as a “tab” 55, but for the sake of consistency with later embodiments inthis application shall be referred to as “lip” 55. The lower or bottomside edges 51 a and 52 a of lips 55 have moved up slightly alongsupporting faces 51 b and 52 b of the sheet on the opposite sides of theslit opposite to lips 55. This displacement of lip edges 51 a and 52 amay be better seen in connection with the sheet when it is bent to agreater degree, for example, when bent to the position shown in FIG. 4C.

[0114] In FIG. 4C it will be seen that edges 51 a and 52 a have movedupwardly on supporting faces 51 b and 52 b of sheet 41 on opposite sidesof bend line 45. Thus, there is sliding contact between edges 51 a and52 a and the opposing supporting faces 51 b and 52 b of the slit duringbending. This sliding contact will be occurring at locations which areequidistant on opposite sides of central bend line 45 if longitudinalslit segments 51 and 52 are formed in equally spaced positions onopposite sides of bend line 45, as shown in FIG. 4A. Sliding contactalso can be facilitated by a lubricant or by adhesives or sealants priorto their setting up or bonding.

[0115] The result of this structure is that there are two actual bendingfulcrums 51 a, 51 b and 52 a, 52 b spaced at equal distances from, andon opposite sides of, bend line 45. Lip edge 51 a and supporting face 51b, as well as lip edge 52 a and supporting face 52 b, produce bending ofbending web 47 about a virtual fulcrum that lies between the actualfulcrums and will be understood to be superimposed over bend line 45.

[0116] The final result of a 90 degree bend is shown in FIG. 4D andcorresponding cross sections 5A . . . -5 c . . . . As will be seen,sheet edge 52 a and bottom side or surface 52 c now are interengaged orrest on, and are supported in partially overlapped relation to,supporting face 52 b (FIG. 5A . . . ). Similarly, edge 51 a and bottomsurface 51 c now engages and rests on face 51 b in an overlappedcondition (FIG. 5B . . . ). Bending web 47 will be seen to have beenplastically deformed or extended along an upper surface of the web 47 aand plastically compressed along a lower surface 47 b of web 47, as bestillustrated in FIG. 5C . . . .

[0117] In the bent condition of FIG. 4D, the lip portions of the sheet,namely, portions 55, which extend over the center line when the sheet isslit, are now resting on supporting faces 51 b and 52 b. Thisedge-to-face engagement and support during the bend, which alternatesalong the bend line in the configuration shown in the drawing, producesgreater precision in bending or folding and gives the bent or foldedstructure greater resistance to shear forces at the bend or fold inmutually perpendicular directions. Thus a load L_(a) (FIG. 5A . . . )will be supported between bending webs 47 by the overlap of the edge 52a and bottom surface 52 c on supporting edge 52 b. Similarly, a load Lb(FIG. 5B . . . ) will be supported by overlap and engagement of the edge51 a and surface 51 c on supporting face 51 b intermediate bending webs47.

[0118] This is referred to herein as “edge-to-face” engagement andsupport of the material along substantially the entire length of oneside of the slit by the material along substantially the entire lengthof the other side of the slit. It will be appreciated that, if sheet 41were bent or folded by more than 90 degrees, edges 51 a and 52 a wouldlift up off the faces 51 b and 52 b and the underneath surfaces 51 c and52 c would be supported by the lower edges of face 51 b and 52 b. If thesheet is bent by less than 90 degrees the edge still comes intoengagement with the face almost immediately after the start of bending,but only the edge engages the face. This support of one side of the sliton the other shall be deemed to be “edge-to-face” engagement and supportas used in the specification and the claims. As will be describedhereinafter, non-ninety degree bends with full support of edges 51 a and52 a by faces 51 b can be achieved by slitting the sheet at angles whichare not at 90 degrees to the sheet.

[0119] While bending straps or webs 47 have residual stresses as aresult of plastic deformation, and while the slits cause a substantialportion of the bend not to be directly coupled together in theslit-based bending system of the present invention, the slits are formedand positioned so as to produce an edge-to-face overlap which provide ssubstantial additional strength to the bent structure over the strengthof the structures of FIGS. 1, 1A and 1B and 2A and 2B, which are basedupon conventional slitting or grooving geometries. The bending straps ofthe present invention, in effect, pre-load the bend so as to pull orclamp the sides of the slit into edge-to-face engagement oversubstantially the entire bending process, and at the end of the bend,over substantially the entire slit length. Pre-loading of the bend bythe residual tension in the strap also tends to prevent vibrationbetween the slit edge which is pre-loaded against the face which acts asa bed on the other side of the slit.

[0120] Moreover, since the edges are interengaged with the faces over asubstantial portion of the length of the slits, loads L_(a) and L_(b)will not crush or further plastically deform bending straps 47, as isthe case for the prior art slitting configuration of FIGS. 2, 2A, 2B.Loading of the present bend is immediately supported by the edge-to-faceengagement produced by the slitting technique of the present invention,rather than merely by the cross sectional connecting area of a twistedand highly stressed strap, as results in the prior art configuration ofFIGS. 2, 2A, 2B and the Gitlin et al. application.

[0121] The embodiment employing laterally stepped or staggered slits ofthe present invention, therefore, result in substantial advantages.First, the lateral position of the longitudinally extending slitsegments 51 and 52 can be precisely located on each side of bend line45, with the result that the bend will occur about a virtual fulcrum asa consequence of two actual fulcrums equidistant from, and on oppositesides of, the bend line. This precision bending reduces or eliminatesaccumulated tolerance errors since slit positions can be very preciselycontrolled by a cutting device which is driven by a CNC controller.

[0122] It also should be noted, that press brakes normally bend byindexing off an edge of a sheet or an existing bend, or otherfeature(s). This makes bending at an angle to the sheet edge feature(s)difficult using a press brake. Bending precisely at angles to anyfeature(s) of the sheet edge, however, can be accomplished readily usingthe present slitting process. Additionally, the resulting bent sheet hassubstantially improved strength against shear loading and loading alongmutually perpendicular axes because the overlapped edges and facesproduced by the present slit configurations support the sheet againstsuch loads.

[0123] As can be seen, the embodiment of the present invention, as shownin FIGS. 3-5C . . . produces precision bending of straps 47 which aresubstantially perpendicular to the bend line. Such an orientation of thebending straps produces significant plastic elongation along the outsideor top surface of the strap, as well as significant compression alongthe inside or bottom surface of the strap. The bend occurs on therelatively short perpendicular straps in a manner similar to the bendsof the perpendicular straps of FIGS. 1-1B, but in FIGS. 3-5C′″ the lip55 of one plane is tucked into interlocking or interengaged relationshipwith the face of the other plane for increased bend strength.

[0124] The prior art approach shown in FIGS. 2-2B orients the connectingstraps 34 parallel to the bend line and results in significant plastictwisting deformation of the straps. Also this plastic twistingdeformation significantly changes the microstructure of the materialaround the bend line. Moreover the straps do not fully tuck or clamp theopposite sides of the sheet into interengaged relation over the lengthof the slits. Still further in the embodiment of FIGS. 3-5C′″ the strapwidth can be varied independently of the jog distance between slits 51and 52 so that greater flexibility in design of the bend strength can beachieved.

[0125] While bending of sheet material by 90 degrees has beenillustrated in the drawing, it will be understood that most of theadvantages described in all embodiments of the present invention alsocan be realized if the slit sheet is bent by more or less than 90degrees. The lip which extends across the bend line will slide onto andengage the opposite face beginning at small bend angles, and suchsupport and engagement will continue at large, 90 degree plus, bendangles.

[0126] It has been found that the embodiment of FIGS. 3-5C′″ is bestsuited for use with relatively ductile sheet materials. As the materialbecomes harder and less ductile, a second embodiment is preferred.

[0127] In the embodiment of the present invention shown in FIGS. 6-8B aslitting configuration is employed which tucks or clamps the sheetmaterial into interengaged relation on both sides of the slits, and alsoreduces bending strap plastic deformation and the residual stress in thestraps. Moreover, this embodiment also allows the strap width to bevaried independently of the jog distance between slits and to have thestrap width increase in both directions from the bend line for lessstress concentration in the connected portions of the sheet of materialon opposite sides of the bend line.

[0128] A bending strap which is oblique to the bend line is employed,which allows the strap length to be increased, as compared to theshorter bending straps of FIGS. 3-5C′″. Plastic deformation also isaccomplished in part by twisting, rather than purely by bending, as isthe case in FIGS. 3-5C′″, but the amount of twisting is greatly reduced,as compared to the parallel straps of FIGS. 2-2B. Moreover, the materiallips on opposite sides of the slit are tucked into interengagement withthe faces over virtually the entire length of the slit so thatsubstantial additional strap stress on loading does not occur.

[0129] Additionally, in the embodiment shown in FIGS. 6-8B, the slitconfiguration produces a continuous sliding interengagement betweenmaterial on opposite sides of the slits during bending, whichinterengagement progresses along the slit from the middle toward theends. The faces on one side of the slits act as beds for sliding supportduring the bend, which results in a more uniform and a less stressfulbending of the bending straps. The embodiment as shown in FIGS. 6-8B,therefore, can be used with sheet material that is less ductile, such asheat treated 6061 aluminum or even some ceramics, and with thickersheets of material.

[0130] Referring specifically to FIGS. 6-8B, a sheet of material 241 tobe bent or folded is formed with a plurality of longitudinally extendingbending strap-defining structures, such as slits 243, along a bend line245. Each of slits 243 optionally may be provided with enlargedstress-relieving end openings 249, or a curved end section 249 a, whichwill tend to cause any stress cracks to propagate back into slits 243,depending on the loading direction of the sheet. As will be seen, theslits of the embodiment of FIGS. 6 and 8B are not stepped, but they areconfigured in a manner producing bending and twisting of obliquelyoriented bending straps 247 about a virtual fulcrum superimposed on bendline 245. The configuration and positioning of the slits, includingselection of the jog distance and kerf width, also causes the sheetmaterial on opposite sides of the slits to tuck or to move into anedge-to-face interengaged relationship during bending. Most preferablyedge-to-face interengagement occurs throughout the bend to itscompletion. But, the jog distance and kerf can be selected to produceedge-to-face interengagement only at the start of the bend, which willtend to insure precise bending. Thus, as used herein, the expression“during bending” is meant to include edge-to-face interengagement at anystage of the bend.

[0131] While the embodiments shown and described in FIGS. 6-8B and 9-10Aare not stepped, the oblique straps of the embodiments of 6-8B and 9-10Acan be combined with the stepped slit configuration of FIGS. 3-5C . . .. Thus, one or both of the ends of the stepped slits can be oblique orcurved.

[0132] As shown in FIG. 6, pairs of elongated slits 243 are preferablypositioned on opposite sides of and proximate to bend line 245 so thatpairs of longitudinally adjacent slit end portions 251 on opposite sidesof the bend line define a bending web, spline or strap 247, which can beseen to extend obliquely across bend line 245. “Oblique” and“obliquely,” as will be explained in more detail below in connectionwith FIG. 11, shall mean that the longitudinal central axis of the strapcrosses the desired bend line at an angle other than 90 degrees. Thus,each slit end portion 251 diverges away from bend line 245 so that thecenter line of the strap is skewed or oblique and bending, as well astwisting of the strap, occurs. Although not an absolute requirement toeffect bending in accordance with the present invention, it will be seenthat slits 243 are longitudinally overlapping along bend line 245.

[0133] Unlike slits 31 in FIGS. 2-2B and the prior art Gitlin, et al.Application, which are parallel to the bend line in the area definingbending straps 34, the divergence of the slits 243 from bend line 245results in oblique bending straps that do not require the extremetwisting present in the prior art of FIGS. 2-2B and Gitlin et al.Application. Moreover, the divergence of slits 243 from bend line 245results in the width dimension of the straps increasing as the strapsconnect with the remainder of sheet 241. This increasing width enhancesthe transfer of loading across the bend so as to reduce stressconcentrations and to increase fatigue resistance of the straps.

[0134] As was the case for the first embodiment, slit kerfs 243preferably have a width dimension, and the transverse jog distanceacross the bend line between slits is dimensioned, to produceinterengagement of sheet material on opposite sides of the slits duringbending. Thus, slits 243 can be made with a knife and have essentially azero kerf, or they can have a greater kerf which still producesinterengagement, depending upon the thickness of the sheet being bent.Most preferably the kerf width is not greater than about 0.3 times thematerial thickness, and the jog distance is not greater than about 1.0times the material thickness.

[0135] As was the case for the embodiment of FIGS. 3-5C . . . , a lipportion 253 extends across bend line 245 to slit 243. Lip 253 slides orrides up a face 255 of a tongue 260 on the other side of slit 243 if thekerf width and jog distance, relative to the thickness of the material,are not so large as to prevent contact between the two sides of the slitduring bending.

[0136] If the kerf width and jog distance are so large that contactbetween the lip portion 253 and face 255 of tongue 260 does not occurthe, bent or folded sheet will still have some of the improved strengthadvantages of oblique bending straps, but in such instances there are noactual fulcrums for bending so that bending along bend line 245 becomesless predictable and precise. Similarly, if the strap-definingstructures are grooves 243 which do not penetrate through the sheet ofmaterial, the grooves will define oblique, high-strength bending straps,but edge-to-face sliding will not occur during bending unless the grooveis so deep as to break-through during bending and become a slit. Thus,arcuately or divergently grooved embodiments of the bending straps willhave improved strap strength even if edge-to-face bending does notoccur.

[0137] Another problem which will be associated with a kerf width thatis too wide to produce interengagement of lips 253 with faces 255 oftongues 260 is that the resultant bent sheet material will not have alip edge supported on a slit face, unless the bend is relatively extremeso as to define a small arcuate angle between the two sides of the bentsheet. As noted in connection with the prior art slitting approach, thiswill result in immediate further stressing of the bending straps uponloading. The problem would not be as severe in the strap configurationof FIGS. 6-8B as in the prior art, but the preferred form is for thekerf width and jog distance to be selected to insure interengagement ofthe lip and tongue face substantially throughout the bending process.

[0138] It is also possible for the slits 243 to actually be on the bendline or even across the bend line and still produce precise bending fromthe balanced positioning of the actual fulcrum faces 255 and the edgesof lips 253 sliding therealong. A potential disadvantage of slits 243being formed to cross the bend line 245 is that an air-gap would remainbetween edge 257 and face 255. An air-gap, however, may be acceptable inorder to facilitate subsequent welding, brazing, soldering, adhesivefilling or if an air-gap is desired for venting. Slit positioning tocreate an air-gap is a desirable feature of the present invention whensubsequent bend reinforcement is employed. Unfilled, however, an air-gapwill tend to place all of the load bearing requirements of the bend inall degrees of freedom, except rotation, on the connected zone or crosssectional area of plastically deformed strap 247. It is also possible toscale slits that cross the bend line that produce edge-to-faceengagement without an air gap.

[0139]FIGS. 7, 8, 8A and 8B illustrate the sheet 241 as bent to a 90degree angle along bend line 245. As best may be seen in FIGS. 8A and8B, an inside edge 257 of lip 253 has slid up on face 255 of tongue 260on the opposite side of the slit and is interengaged and supportedthereon. A vertical force, F_(v), therefore, as shown in FIG. 8A issupported by the overlap of edge 257 on face 255. A horizontal force,F_(H), as shown in FIG. 8B similarly will be resisted by the overlap ofedge 257 on face 255. Comparison of FIGS. 8A and 8B to the prior artFIGS. 1A, 1B and 2A and 2B will make apparent the differences which thepresent bending method and slit configuration have on the strength ofthe overall structure. The combination of alternating overlappingedge-to-face support along the slits and the oblique bending straps,which are oblique in oppositely skewed directions, provides a bend andtwist which is not only precise but has much less residual stress andhigher strength than prior slitting configurations will produce.

[0140] However, skewing of the bending straps in opposite directions isnot required to achieve many of the advantages of the present invention.When sheet 241 is an isotropic material, alternate skewing of the straplongitudinal central axes tends to cancel stress. If the sheet materialis not isotropic, skewing of the oblique straps in the same directioncan be used to negate preferential grain effects in the material.

[0141] Alternatively, for isotropic sheet material, skewing of thestraps in the same direction can produce relative shifting along thebend line of the portions of the sheet on opposite sides of the bendline, which shifting can be used for producing a locking engagement witha third plane such as an interference fit or a tab and slot insertion bythe amount of side shift produced.

[0142] The geometry of the oblique slits is such that they bend andtwist over a region that tends to reduce residual stress in the strapmaterial at the point where the slit is terminated or the strapconnected to the rest of the sheet. Thus, crack propagation is reduced,lessening the need for enlarged openings or curls at the slit ends. Ifthe resultant structure is intended primarily for static loading or isnot expected to be loaded at all, no stress reducing termination isrequired in the arcuate slit that produces the oblique strap.

[0143] Moreover, it will be understood that slits 243 can be shiftedalong bend line 243 to change the width of straps 247 without increasingjog distance at which the slits are laterally spaced from each other.Conversely, the jog distance between slits 243 can be increased and theslits longitudinally shifted to maintain the same strap thickness.Obviously both changes can be made to design the strap width and lengthto meet the application.

[0144] Generally, the ratio of the transverse distance from slit toslit, or twice the distance of one slit to the bend line is referred toas the “jog”. The ratio of the jog distance relative to the materialthickness in the preferred embodiments of the present invention will beless than 1. That is, the jog distance usually is less than one materialthickness. A more preferred embodiment makes use of a jog distance ratioof less than 0.5 material thickness. A still more preferred embodimentmakes use of a jog distance ratio of approximately 0.3 materialthickness, depending upon the characteristics of the specific materialused and the widths of the straps, and the kerf dimensions.

[0145] The width of bending straps 247 will influence the amount offorce required to bend the sheet and that can be varied by either movingslits 243 farther away from the bend line 245 or by longitudinallyshifting the position of the slits, or both. Generally, the width ofoblique bending straps 247 most preferably will be selected to begreater than the thickness of the material being bent, but strap widthsin the range of about 0.5 to about 4 times the thickness of the materialmay be used. More preferably, the strap width is between 0.7 and 2.5times the material thickness.

[0146] One of the advantages of the present invention, however, is thatthe slitting configuration is such that bending of sheets can normallybe accomplished using hand tools or tools that are relatively lowpowered. Thus, the bending tools need only so much force as to effectbending and twisting of bending straps 247; they do not have to havesufficient power so as to control the location of the bend. Such controlis required for powered machines, such as press brakes, which clamp thematerial to be bent with sufficient force so as to control the locationof the bend. In the present invention, however, the location of the bendis controlled by the actual fulcrums, namely edges 257 pivoting on face255 on opposite sides of the bend line. Therefore, the bending toolrequired need only be one which can effect bending of straps 247, notpositioning of the bend. This is extremely important in applications inwhich high strength power tools are not readily available, for example,in outer space or in the field fabrication of structures or atfabricators who do not have such high-powered equipment. It also allowslow-force sheet bending equipment, such as corrugated cardboard bendingmachines, bladders, vacuum bending, hydraulic pulling cylinders withfolding bars, and shape-memory bending materials, to be used to bendmetal sheets, as will be set forth in more detail below. Additionally,strong, accurate bends are important in the fabrication of structures inwhich physical access to power bending equipment is not possible becauseof the geometry of the structure itself. This is particularly true ofthe last few bends required to close and latch a three-dimensionalstructure.

[0147] The most preferred configuration for slit end portions 251 is anarcuate divergence from bend line 245. In fact, each slit may be formedas a continuous arc, as shown in FIGS. 9, 10 and 10A and describedbelow. An arc causes the material on the side of the slit to smoothlyand progressively move up the face side of the tongue along an arcuatepath beginning at center of the slit and progressing to the ends of theslit. This reduces the danger of hanging up of edge 257 on face 255during bending and thereby is less stressful on the bending straps.Additionally, large radii of cut free surfaces are less prone to stressconcentration. In the configuration of FIGS. 6-8B, the central portionof slits 243 is substantially parallel to bend line 245. Somenon-parallel orientations, particularly if balanced on either side ofthe bend line, may be acceptable and produce the results describedherein.

[0148] It also would be possible to form end portions 251 to divergefrom bend line 245 at right angles to the bend line and the center ofslits 243. This would define a bending strap that could be non-oblique,if the slits did not longitudinally overlap. The disadvantage of thisapproach is that the bending straps 247 tend not to bend as uniformlyand reliably and thereby influence the precision of the location of thebend. Additionally, such a geometry eliminates twisting of the strap andinduces severe points of stress concentration on the inner and outerradii of the bend and may limit the degree of edge-to-edge engagement.

[0149] The bending straps in all the embodiments of the presentinvention are first elastically deformed and in plastic/elasticmaterials thereafter plastically deformed. The present slittinginvention also can be used with elastically deformable plastics thatnever plastically deform. Such materials would be secured in a bent orfolded condition so that they do not resiliently unbend. In order tomake it more likely that only elastic deformation occurs, it ispreferable that the bending straps be formed with central longitudinalstrap axes that are at a small angle to the bending line, mostpreferably, 26 degrees or less. The lower the angle, the higher thefraction of twisting that occurs and the lower the fraction of bendingthat occurs. Moreover, the lower the angle, the higher the bendingradius that occurs. Rigid materials that do not gracefully deformplastically, such as rigid polymers, rigid metal, the more flexibleceramics and some composites, can tolerate a large bending radius in theelastic regime. They can also tolerate a torsion or twisting springaction that is distributed over a long strap of material. Low anglestraps provide both aspects.

[0150] At the end of the bend of a plastically deformed sheet, however,there will remain a certain resilient elastic deformation tending topull edge 257 down against face 255 and resulting in residual resilientclamping force maintaining the interengagement between material onopposite sides of the slits. Thus, the elastic resiliency of the sheetbeing bent will tend to pre-load or snug down the overlapping sheetedges against the supporting faces to ensure strength at the bend andreduce bending strap incremental stress on loading of the bend.

[0151] The embodiment shown in FIGS. 9, 10 and 10A is a special case ofthe oblique strap embodiment described in connection with FIGS. 6-8B.Here the oblique straps are formed by completely arcuate slits 443. Thisslit configuration, shown as a circular segment, is particularly wellsuited for bending thicker and less ductile metal sheets, for example,titanium and ¼ inch steel plate and up.

[0152] When arcuate or circular slits 443 are formed in sheet 441 onopposite sides of bend line 435, lip portions 453 of the sheet, whichextend over bend line 445 to slits 443, begin tucking or sliding ontoface 455 of the tongues 470 at a center of each arcuate slit at thestart of bending. Lip portions 453 then slide from the center of eachslit partially up onto tongue faces 455 progressively toward the slitends as straps 447 are twisted and bent. The progressive tucking of thelips onto the opposing faces is less stressful on the slit ends 449, andtherefore more suitable for bending of less ductile and thickermaterials, than say the embodiment of FIGS. 6-8B, in which the slitshave straight central portions and simultaneously slide up onto thefaces over the entire straight portion.

[0153] Slit ends 449 in FIG. 10 do not have the stress-relievingopenings 249, nor radiused ends 249 a of FIGS. 6-8 nor the curved endsof FIG. 11, but slits 443 are more economical to cut or form into mostsheet stock. Moreover, the deformation of straps 447 is more gradualduring bending so that stress concentration will be reduced. This, ofcourse, combines with increasing strap width to transfer loading forcesand bending forces more evenly into the remainder of the sheet withlower stress concentration.

[0154] The various embodiments of the present sheet slitting andgrooving invention allow designing manufacturing and fabricationadvantages to be achieved which have not heretofore been realized. Thus,the full benefits of such design and fabrication techniques as CADdesign, Rapid Prototyping and “pick and place” assembly can be realizedby using sheet stock formation techniques in accordance with the presentinvention. Moreover, standard fabrication techniques, such as welding,are greatly enhanced using the strap-defining configurations of thepresent invention.

[0155] The many advantages of using sheets formed in accordance with thepresent invention can be illustrated in connection with a manufacturingtechnique as basic as welding. Sheet bending using the present method,for example, avoids the manufacturing problems associated with handlingmultiple parts, such as jigging.

[0156] Additionally, the bent sheets of the present invention in whichslitting is employed can be welded along the slits. As can be seen inFIG. 10A, for example, face 455 and end surface 457 of tab 453 form aV-shaped cross section that is ideal for welding. No grinding ormachining is required to place a weld 460 (broken lines) along slits 443as shown in FIG. 10A. Moreover, the edge-to-face engagement of the sidesof the sheet on opposite sides of the slits, in effect, provides a jigor fixture for holding the sheet portions together during the weld andfor reducing thermally induced warping. Set up time is thereby greatlyreduced, and the dimensional accuracy achieved by the present slittingprocess is maintained during the welding step. The arcuate slits alsoprovide an easily sensed topographic feature for robotic welding. Theseadvantages also accrue in connection with soldering, brazing andadhesive filling, although thermal distortion is usually not a seriousissue for many adhesives.

[0157] Filling of the slits by welding, brazing, soldering, pottingcompound or adhesives allows the bent sheets of the present invention tobe formed into enclosures which hold fluids or flowable materials. Thus,bent sheet enclosures can even be used to form fluid-tight molds, withthe sheeting either being removed or left in place after molding.

[0158] One of the significant advantages of using oblique, andparticularly curved, grooves or slits is that the resulting bendingstraps are diverging at the point at which they connect to the reminderof the sheet material. Thus, area 450 of strap 447 in FIG. 10 istransversely diverging between slit end 449 and the next slit 443. Thisdivergence tends to deliver or transfer the stresses in strap 447 ateach end into the remainder of the sheet in a diffused or unconcentratedmanner. As the arc or radius of the slits is reduced the divergenceincreases, again allowing a further independent tailoring of the strapstress transfer across the bend. Such tailoring can be combined with oneor more of changes to strap width, jog distance and slit kerf to furtherinfluence the strength of the bend. This principle is employed in thedesign of the slits on grooves of FIG. 11.

[0159] While the oblique bending straps of the embodiments of FIGS. 6-8and FIGS. 9-10 result in substantial improvements of the overallstrength and fatigue resistance of the bent structure, it has been foundempirically that still further improvements, particularly in connectionwith fatigue, can be achieved if the strap-defining structure takes theform of an arcuate slit. As used herein, “arcuate” shall mean andinclude a circular arc and a series of longitudinally connected,tangential arcs having differing radii. Preferably, the arcuate slits orgrooves have relatively large radii (as compared to the sheetthickness), as illustrated in FIG. 11. Thus, a sheet of material 541 canbe provided with a plurality of connected, large radii, arcuate slits,generally designated 542, along bend line 543. Arcuate slits 542preferably are longitudinally staggered or offset (by an offset distancemeasured between the centers of adjacent slits along bend line 543 andalternatively are on opposite sides of the bend line 543, in a mannerdescribed above in connection with other embodiments of the presentinvention. Arcuate slits 542 define connected zones, which are bendingstraps 544, and disconnected zones, which are provided by slits 542.Only the right hand slit 542 in FIG. 11 shows a kerf or slit thickness,with the remainder of the slits 542 being either schematically shown ortaking the form of a slit form by a knife resulting in no kerf.

[0160] Longitudinally adjacent slits 542 defined therebetween bendingstraps 544, which are shown in this embodiment as being oblique tobending line 543 and skewed in alternating directions, as also describedabove. Each slit 542 tends to have a central arcuate portion 546 whichdiverges away from bending line 543 from a center point 547 of thearcuate slit. End portions 548 also may advantageously be arcuate with amuch smaller radius of curvature that causes the smiles to extend backalong arc portion 549 and finally terminated in an inwardly arc portion551.

[0161] It will be seen, therefore, that bending strap 544 is defined bythe arc portions 546 on either side of bending line 543 and at the endof the straps by the arcuate end portions 548. A minimum strap widthoccurs between the arcuate slit portions 546 at arrows 552 (shown inFIG. 11 at the left hand pair of longitudinally adjacent slits). If acenter line 553 is drawn through arrows 552 at the minimum width of thestrap, it would be seen that the center line crosses bend line 543 atabout the minimum strap width 552. Strap 544 diverges away fromlongitudinal strap axis 553 in both directions from minimum strap width552. Thus, a portion 554 of the sheet on one side of bend line 543 isconnected to a second portion 556 of the sheet on the opposite side ofbend line 543 by strap 544. The increasing width of strap 544 in bothdirections from the minimum width plane 552 causes the strap to beconnected to the respective sheet portions 554 and 556 across the bendline in a manner which greatly reduces stress and increases fatigueresistance.

[0162] For purposes of further illustration, strap 544 a has been crosshatched to demonstrate the increasing width of the strap along itscentral longitudinal strap axis 553. Coupling of sheet portion 554 by anever-increasing strap width to sheet portion 556 by a similarlyincreasing strap width tends to reduce stress. Orienting the centrallongitudinal axes 553 of straps 554 at an oblique angle to bend line 543results in the straps being both twisted and bent, rather than solelytwisted, which also reduces stresses in the straps. Stresses in thesheet flow across the bend through the connected material of the strap.Cyclical stress in tension, the primary cause of fatigue failure, flowthrough the twisted and bent strap and generally parallel to large radiiarcs 546 and 549. The smaller radii of arcs 551 and 548 provide a smoothtransition away from the primary stress bearing free surfaces of 546 and549 but do not themselves experience significant stress flow. In thisway, the arcuate slits are like portions of very large circles joinedtogether by much smaller circles or arcs in a way that positions onlythe large radii arcs (compared to the material thickness) in the stressfield flow, and uses smaller radii arcs as connectors to minimize thedepth into the parent plane away from the fold line that the slit isformed. Thus, slit ends, at which stress caused micro cracking is mostlikely to occur, will tend not to be propagated from one slit to anotherdown the length of the bend, as can possibly occur in a failurecondition in the embodiments of FIGS. 6-8 and 9-10.

[0163] The bending strap shape also will influence the distribution ofstresses across the bend. When the bending strap diverges relativelyrapidly away from the narrowest strap width dimension, e.g., widthdimension 552 in FIG. 11, there is a tendency for this minimum dimensionto act as a waist or weakened plane at the center of the strap. Suchrapid narrowing will allow localized plastic deformation and stressconcentration in the strap, rather than the desired distribution of thestresses over the full length of the strap and into the sheet material554 and 556 on either side of the strap.

[0164] As shown in FIG. 11, and as is preferred, strap 544 preferably aminimum width dimension 552 providing the desired strap strength andthen gradually diverge in both directions along the strap with any rapiddivergence taking place as the strap terminates into the sheet portions554 and 556. This construction avoids the problem of having an undulynarrow strap waist at 552 which will concentrate bending and twistingforces and produce failure, rather than distributing them evenly alongthe length of the strap and into sheet portions 554 and 556.

[0165] The tongue side of a slit, that is, the portion of the parentplane defined by the concave side of the arcuate slit, tends to beisolated from tensile stress. This makes the tongue ideal for locatingfeatures that cut into the parent plane. Attachment or alignment holes,or notches that mate with other connecting geometry are examples. FIG.11A illustrates positioning of water-jet cut or laser cut, rapidpiercing holes 560 and 565 on the tongue 555 of slit 546. Rapid pierceholes are somewhat irregular and elsewhere might initiate a crackfailure in fatigue. In FIG. 11A two alternative locations of rapidpiercing holes are shown. Rapid pierce holes are important to reduce thetotal cost of laser or water-jet cutting because slow piercing is verytime consuming.

[0166] One of the most beneficial aspects of the present invention isthat the design and cutting of the material to form the straps and theedge-to-face engagement of the lips and tongues of the slits isaccomplished in a manner in which the microstructure of the materialaround the bend or fold is essentially unchanged in comparison to thesubstantial change in the microstructure of materials bent or folded tothe same angle or degree of sharpness using conventional bendingtechniques, as described in the prior art. It is the relationship of thestraps and the edge-to-face engagement of the slits which provides acombination of twisting and bending deformation when the material isbent that greatly reduces the stress around the bend and leaves themicrostructure of the material around the bend essentially unchanged.When conventional bending techniques of the prior art are used there isa substantial change in the microstructure of the material around thebend if the bend is made to be sharp (for example, 90 degrees on theinside of the bend, as shown for example in FIGS. 5A . . . , 8, 8A, 8Band 10A.

[0167] As was generally described in connection with other embodimentsof the present invention, slits 542 can have their geometries altered toaccommodate a wide range of sheet characteristics. Thus, as the type ofsheet material which is bent is altered, or its thicknesses changed orstrength characteristics of the bend are to be tailored, the geometry ofsmile slits 542 can also change. The length, L, of each slit can change,as can its offset distance, O.D., or longitudinal spacing along bendline 543. The height, H, of the slits can also be changed, and the jogdistance, J, across the bend line between slits on opposite sides of thebend line can be altered. These various factors will have an effect onthe geometry and orientation of straps 544, which in turn will alsoeffect the strength of the bend and its suitability for use in variousstructures. Of equal importance is the shape of the arcuate slit inconjunction with the aforementioned sealing and positioning variable.

[0168] It is a feature of the present invention, therefore, that thestrap-defining slits or grooves can be tailored to the material beingbent or folded and the structure to be produced. It is possible, forexample, to empirically test sheets of a given material but differingthicknesses with arc slit designs in which the geometries have beenchanged slightly, but the designs comprise a family of related arcgeometries. This process can be repeated for differing materials, andthe empirical data stored in a database from which designs can beretrieved based upon input as to the sheet of material being bent andits thickness. This process is particularly well suited for computerimplementation in which the physical properties of the sheet of materialare entered and the program makes a selection from the computer databaseof empirical data as to the most appropriate arc geometry for use inbending the material. The software can also interpolate betweenavailable data when the sheet is of a material for which no exact datais stored or when the sheet has a thickness for which there are no exactstored data.

[0169] The design or configuration of the arcs, and thus the connectingstraps, also can be varied along the length of a bend line toaccommodate changes in the thickness of the sheet of material along thebend line. Alternatively, strap configurations along a bend line canchange or be tailored to accommodate non-linear loading. While not asimportant as the strength and fatigue-resistance improvements of thepresent invention, the slit or strap configurations also can be variedto provide different decorative effects in combination with improvedstrength and fatigue resistance.

[0170] Another advantage which accrues from the various embodiments ofthe sheet slitting system of the present invention is that the resultingbends or fold are relatively sharp, both internally and externally.Sharp bends enable strong coupling of one bent structure to anotherstructure. Thus, a press brake bend tends to be rounded or have anoticeable radius at the bend. When a press brake bent structure iscoupled to a plate, for example, and a force is applied tending torotate the bent structure about the arcuate bend, the bent structure candecouple from the plate. Such decoupling can occur more easily than ifthe bend were sharp, as it will be for the bends resulting from usingthe present slitting scheme.

[0171] The ability to produce sharp or crisp bends or folds allows theprocess of the present invention to be applied to structures which hadheretofore only been formed from paper or thin foils, namely, to thevast technology of origami or folded paper constructions. Complexthree-dimensional folded paper structures, and a science or mathematicsfor their creation, have been developed after centuries of effort. Suchorigami structures, while visually elegant, usually are not capable ofbeing formed from metal sheets of a thickness greater than a foil. Thus,origami folded sheets usually cannot support significant loading.Typical examples of origami are the folded paper constructions set forthin “ADVANCED ORIGAMI” by Dedier Boursin, published by Firefly Books,Buffalo, N.Y. in 2002, and “EXTREME ORIGAMI” by Kunihiko Kasahara,published by Sterling Publishing Company, NY, N.Y. in 2002. The presentinvention thus enables a new class of origami-analog designs in whichthe slitting and bending methods described herein are substituted fororigami creases.

[0172] The sheet slitting or grooving process of the present inventionproduces sharp bends and even allows the folding of metal sheets by 180degrees or back on itself. Thus, many structurally interesting origamiconstructions can be made using sheet metal having a thickness wellbeyond that of a foil, and the resulting origami-based structure will becapable of supporting significant loads.

[0173] Another interesting design and fabrication potential is realizedby using the present slitting configurations in connection with RapidPrototyping and Rapid Manufacturing, particularly if automated “Pick andPlace” component additions are employed. Rapid Prototyping and RapidManufacturing are broadly known and are comprised of the use of CAD(computer-assisted design) and CAM (computer-assisted manufacturing)design, respectively, to enable three-dimensional fabrication. Thedesigner begins with a desired virtual three-dimensional structure.Using the current invention to enable Rapid Prototyping, the CADsoftware unfolds the three-dimensional structure to a two-dimensionalsheet and then locates the slit positions for bending of the sheet toproduce the desired structure. The same can be done in RapidManufacturing using CAM. Other types of software for performing similartasks. The ability to precisely bend, and to tailor the bend strength,by selecting jog distances and bending strap widths, allows the designerto layout slits in the unfolded two-dimensional sheet drawing in thedesign process, which thereafter can be implemented in the manufacturingprocess by sheet grooving or slitting and bending to produce complexthree-dimensional structures, with or without add-on components.

[0174] Broadly, it is also known to assemble components onto circuitboards for electronic devices using high speed “pick and place”automated component handling techniques. Thus, assembly robots can pickcomponents from component supply devices and then place them on acircuit board or substrate or chassis. The robotics secure thecomponents to the substrate using fasteners, soldering plug-ins or thelike. Such “pick and place” assembly has been largely limited to placingthe components on a flat surface. Thus, the circuit boards must beplaced in a three-dimensional housing after the “pick and place”assembly has been completed.

[0175] An electronic housing, usually cannot be folded or bent into athree-dimensional shape after components are secured to the walls of thehousing. Moreover, prior techniques for bending have lacked theprecision possible with the present invention and necessary to solvecomponent or structural alignment problems. Pre-folding or bending upthe housing has, therefore, limited the ability for pick and placerobotics to be used to secure electronic components in the housings.

[0176] It also should be noted that the straps present between slits canbe advantageously used as conductive paths across bends in electronicapplications, and the precision possible allows conductive paths orcomponents on the circuit board to be folded into alignment when thethree-dimensional chassis is formed, or when circuit boards themselvesare folded into a more dense conformation.

[0177] The design and manufacturing processes of the present invention,however, enable precision bends to be laid out, slit and then formedwith relatively low forces being involved, as is illustrated in FIGS.28A-28E. Thus, a housing can be designed and cut from a flat sheet 821and high-speed pick and place robotics used to rapidly securecomponents, C, to any or all six walls of a cube enclosure, and thehousing or component chassis can be easily bent into a three-dimensionalshape after the pick and place process is completed.

[0178] As shown in FIG. 28A, sheet 821 has component C secured theretobefore bending, preferably by high-speed robotic techniques. Sheet 821is formed by laser cutting, water jet cut, die cutting or the like withthe designed cutout features 822, component-receiving openings 823, tabs824 and support flanges 826 and tab-receiving slots 827. In FIG. 28Bsheet 821 has been bent along bend line 831, causing a tab 824 to bedisplaced outwardly. The sheet is next bent along bend line 832 in FIG.28C and then bent over component C along bend line 833 in FIG. 28D,while side flange 826 has been bent along bend line 834. Finally,chassis end portion 836 is bent upwardly along bend line 837 and tabs824 are inserted into slots 827 so as to enable rigid securement of thesheet into a three-dimensional electronics chassis 838 around componentC.

[0179] Obviously, in most cases a plurality of components C would besecured to sheet 821 before bending, and components C also can besecured to chassis 838 at various steps in the bending process and tovarious surfaces of the chassis.

[0180] FIGS. 28A-28E also illustrate a fundamental design process whichis implemented by the sheet bending method of the present invention. Oneof the most space-efficient ways of supporting components is to mountthem on sheet stock. Using conventional sheet stock bending techniques,however, does not enable tight bends and intricate inter-leaved sheetportions. The bending process of the present invention does, however, byreason of the ability to lay out slits extremely accurately that willproduce bend in precise locations so that openings, cutouts, slots, tabsand the like will precisely align in the bent structure, as well asmounted components and the coupling to other structures.

[0181] Moreover, the precise layout of bending lines and chassis orenclosure features is only part of the advantage. The structure itselfcan be bent using relatively low force, and even by means of hand tools.The combination of precision location of bend lines and low-forcebending enables a design technique which was only heretofore partiallyrealized. The technique involves selecting components having the desiredfunctions and positioning them in space in a desired arrangement.Thereafter, a chassis is designed with supporting thin sheet portions ofthe chassis necessary to support the components as positioned beingdesigned, for example, using CAD techniques. The bend lines are locatedto produce the supporting sheet portions, and the chassis unfoldedgraphically to a flat sheet with the necessary feature and fold lines,as shown in FIG. 28A.

[0182] While such techniques have been described before in CAD designliterature, and CAD and CAM software programs, they have not heretoforebeen effectively implemented in anything but the most simple designsbecause precision, low-force bending of sheet metals was not practical.The present slitting-based invention enables practical fabrication ofthis theoretical CAD or CAM design technique. Prior art CAD or CAMdesigns could not previously be physically realized in real materials tothe same accuracy as the theoretical CAD or CAM model because, forexample, conventional bending tolerances could not be held. Theprecision of bending possible with the present invention dramaticallyincreases the correspondence between the CAD or CAM model and theachievable physical form for bent sheet materials.

[0183] Moreover, the bending need not take place at the pick and placeor rapid prototyping site. The sheet with attached components can betransported with the components being formed and selected to act asdunnage for the transport process. Once at the fabrication site, whichmay be remote from the design and cutting site, the chassis or housingsheet will be bent precisely, even by hand if desired, and the benthousing secured into a three-dimensional structure, with a plurality ofselected components being secured thereto internally and/or externally.

[0184] Moreover, three-dimensional chassis and other structures also canhave panels therein which are attached by straps along a bend line toprovide doors in the chassis or structure for periodic or emergencyaccess to the interior of the structure. Separate door hinge assembliesare thereby eliminated.

[0185] Using the various embodiments of the sheet slitting or groovingtechniques described herein, an extremely wide range of products can beformed. Without limitation by enumeration, the following are examples ofproducts which can be folded from sheet material using the slitting andgrooving schemes of the present invention: trusses, beams, curved beams,coiled beams, beams within beams, enclosures, polyhedrons, stud walls,beam networks, enveloped beams, flanged beams, indeterminatemultiple-piece flanged beams, machines, works of art and sculpture,origami three-dimensional structures, musical instruments, toys, signs,modular connections, packages, pallets, protective enclosures,platforms, bridges, electrical enclosures, RF shield enclosures, EMIshields, microwave guides and ducts. A few examples of such structuresare shown in FIGS. 12-30 and 32.

[0186] Formation of a curved box beam using the slitting process andslit sheet of the present invention can be described by reference toFIGS. 12, 13 and 14. A sheet of material 561 is shown in FIG. 12 thathas two bend lines 562 and 563. Bend line 562 has a plurality of arcuateslits 563 on opposite sides of bend line 562. Also positioned along bendline 562 are smaller arcuate slits 564. The slits 563 and 564 have thegeneral configuration as described and shown in connection with slits542 in FIG. 11, but the length of slits 564 is reduced relative to thelength of slits 563, and slits 564 will be seen to be positioned at theapex 566 of notches 567 which are provided in the edges 568 of the sheetof material. The bending straps 569 defined by longitudinally adjacentend portions of slits 563 and longitudinally adjacent end portions ofslits 563 and 564 are essentially the same in configuration,notwithstanding differences in the length of the slits 563 and 564.There will be some slight shape difference due to arcuate segmentdifferences, but bending straps 569 will be essentially uniform in theirstrength and fatigue-resistant capabilities along the length of bendingline 562.

[0187] One of the advantages of the placement of slits 564 is that theytend to contain any stress crack propagation, which could occur atapexes 566 of notches 567. The various leaves or fingers 571 defined bynotches 567 can be bent, for example, into or out of the page to a 90degree angle, or to other angles if the structure should require. Thecentral portion 572 can remain in the plane of the sheet on which FIG.12 is drawn.

[0188] A plurality of slits 576 and 577 are positioned along secondbending line 563. These slits have much tighter end curve portions 578than the arc-like slits shown proximate first bend line 562. Generally,the tight curved end portions 578 are not as desirable as the moreopen-ended portions used in connection with slits 563 and 564.Nevertheless, for ductile materials that do not tend to stress fracture,slits of the type shown for slits 576 and 577 are entirely adequate.Again, the difference between slits 576 and 577 is that the smallerslits have been used at the apexes 566 of notches 567.

[0189] Once slit, sheet 561 can be bent along bend line 563 so that theleaves 571 can be bent to an angle such as 90 degrees relative to thecentral portion 572. It should be noted that normally the slits alongbend line 562 and 563 will have the same shape, that is, they willeither be slits 563 and 564 or slits 576 and 577. It is possible to mixslit configurations, but normally there will be no advantage from mixingthem as shown in FIG. 12. The purpose of the illustrated embodiment ofFIG. 12 is to show different slit configurations that are suitable foruse in the bending of sheet material in accordance with the presentinvention.

[0190] The design and formation of a curved box beam using two sheetsslit, as shown in the flat in FIG. 12, can be described in connectionwith FIGS. 13 and 14. The design would be accomplished on a CAD or CAMsystem, as described earlier, and the slits made in sheet 561identically as laid out in the design process on the CAD, CAM or othersystems. A curved box beam, generally designated 581, is shown in whichone designed, cut and bent U-shaped sheet 572 a is secured to a seconddesigned, cut and bent U-shaped sheet 572 b. As will be seen from FIGS.13 and 14, the fingers or leaves 571 a have been folded down over theoutside of the fingers or leaves 571 b. In both cases, the apexes 566are closely proximate the fold lines 562 a, 563 a, 562 b and 563 b. Thisplacement of the apexes allows bending of the sheet, by permittingnotches 567 a to have the included angle of the notches increase, whilethe included angle of notches 567 b decrease in the area 582 of thelongitudinal bending of beam 581. The central portions 572 a and 572 bof the sheet material have a thickness that will accommodate bendingwithout buckling, at least in radii that are not extreme.

[0191] The folded sheets can be secured together by rivets 583 or othersuitable fasteners, adhesives or fastening techniques such as weldingand brazing. Openings for the fasteners can be pre-formed as shown inFIG. 12 at 580. The location of the openings 580 can be precisely set ifthe exact curved configuration is determined or known in advance ofbending, or openings 580 can be positioned in central locations andthereafter used with later drilled holes to join the two bent sheetstogether in a curvature that is indeterminant or established in thefield.

[0192] One application for indeterminant curved box beams, for example,is in the aircraft industry. Difficult to bend 4041 T-6 or 6061 T-6aluminum is designed with the desired layout of slits and then providedin completed slit sheets as shown in FIG. 12. The sheets are then formedin the field to provide a box beam having a curvature which isdetermined in the field, for example, by the curvature of a portion ofan airplane which must be repaired. The two sheets that form the boxbeam are curved to fit under a portion of the skin of the airplane whichhas been damaged, and then the skin is thereafter attached to thecentral section 572 of the curved box beam.

[0193] Bending of the leaves or fingers 571 can be done with simple handtools, or even by hand, and field riveting used to hold the curvature ofthe box beam by using the pre-formed holes 58 as guides for holes thatare drilled in the leaves or fingers of the underlying folded sheet.Thus, with a simple hand drill and pliers, a high-strength structural4041 T-6 aluminum box beam can be custom formed and positioned as anairplane structural component for subsequent fastening of the skin ofthe airplane thereto. This can enable, for example, field repairs undereven combat conditions so that the plane can be flown to a site at whichpermanent repairs can be made.

[0194] When the longitudinally curved box beam has a predetermined orknown longitudinal curvature, leaves or fingers 571 a and 571 b can bedefined by notches in which the fingers interdigitate or mesh with eachother in the same plane. This will produce beam side walls that aresmooth and without openings.

[0195] Box beams, whether curved or straight, also can be used inexoskeletal designs in order to provide high strength-to-weightadvantages. Thus, rather than using a solid beam with its attendantweight, hollow, folded or bent beams can have corresponding strength butlower weight. If desired such hollow beams also can be filled with afoam, including a metal foam.

[0196] As shown in FIGS. 12-14 a longitudinally curved box beam 681 isproduced by bending the sheet material along straight fold lines 562 and563. It is also possible to produce longitudinally curved box beams byslitting or grooving along curved bend lines.

[0197] Turning now to FIGS. 15 and 16, a sheet of material designed andslit or grooved for folding and a three-dimensional structure made fromthe same, respectively, are shown. Sheet 611 has been designed to beslit or grooved along longitudinally extending fold lines 612 and 613.Further slitting and grooving has taken place on transversely extendingfold lines 614, 615, 616 and 617. Opposed side edges 618 of sheets 611are circular, and a plurality of notches 619 are formed in opposite sideedges of the sheet. A coupling tab or flange 621 is formed at one end ofthe sheet and preferably has fastener receiving openings 622 thereinwhich will align with opening 623 in the opposite end of sheet 611.Slits or grooves 624 of the type shown in the embodiment of FIGS. 9 and10 have been positioned along fold lines 612-617. It will be understoodthat slits or grooves of the type shown in other embodiments could beemployed within the scope of the present invention.

[0198] The sheet of material shown in FIG. 15 is designed to envelop orenclose a cylindrical member, such as a rod, post or column 631 shown inFIG. 16. By bending sheets 616 along fold lines 612-617, sheet 611 canbe folded around to enclose cylindrical member 631 as shown in FIG. 16.The circular arcuate portion 618 of the sheet are dimensioned to have aradius which mates with that of column 631. Notches 619 close up and theedges defining the notches abut each other, while the fold lines 614-617allow the sheet to be folded into a square configuration around thecolumn 631. The bent three-dimensional structure which results has aplurality of planar panels 636-639 which provide surfaces against whichother members or structures can be easily attached. Folded sheet 611 maybe secured in place around column 631 by fasteners through openings 622and 623. The configuration of the grooves or slits 624 causes the foldedsheet 611 to become a high-strength, rigid structure around column orpost 631. Securement of folded sheet 611 to post 631 against verticaldisplacement can be the result of an interference fit between arcuateedges 618 and the post, and/or the use of fasteners, adhesives, welding,brazing or the like, and the assembly has many applications which solvethe problem of subsequent coupling of structural members to acylindrical structure. The example of FIGS. 15 and 16 is not only apotential cosmetic cladding, it is a structural transition piece betweencylindrical and rectilinear forms.

[0199] The designed and manufactured slit or grooved sheet and method ofthe present invention also may be used to design and form corrugatedpanel or deck assemblies. FIGS. 17 and 18 illustrate two corrugatedpanel assemblies that can be designed and constructed using theapparatus and methods of the present invention. Such assemblies areparticularly effective in providing high-strength-to-weight ratios, andthe sheet folding techniques of the present invention readilyaccommodate both folding of the corrugated sheet and the provision ofattachment tabs.

[0200] In FIG. 17 attachment tabs are provided which can extend throughslits to couple the corrugated sheet to the planar sheet, while in FIG.18 tabs having fastener receiving openings are provided.

[0201] In FIG. 17, a sheet of material 641 has been slit or groovedalong longitudinally extending fold lines 642-647 in accordance with theteaching of the present invention. Additionally, a plurality of tabs 649have been formed along fold line 643, 645 and 647. Tabs 649 are cut insheet 641 at the same time as formation of the slits or grooves 651along the fold lines. Thus, a U-shaped cut 652 is formed in sheet 641 sothat when the sheet is folded to the corrugated condition shown in FIG.17, the tabs will protrude upwardly. Tabs 649 will extend at an anglefrom the vertical when folding occurs to form the corrugations, but tabs649 can be bent from an angled position to a near vertical position, asshown in 617, by a subsequent step.

[0202] The folded or corrugated sheet 641 shown in FIG. 17 can beattached to a second planar sheet 656 which has a plurality of slits 657formed therein. Slits 657 are positioned and dimensioned to matinglyreceive tabs 649 therethrough. When sheet 656 is lowered down overcorrugated folded sheet 641, tabs 649 will extend up through slits 657.Tabs 649 can be in interference fit with slits 657 to secure the sheetstogether, or tabs 649 can be bent to a horizontal position or twistedabout a vertical axis to secure the two sheets together. Tab 649 alsomay be bent down and secured to sheet 656 by adhesives, welding, brazingor the like.

[0203] Optionally, a second sheet of material, not shown, can beattached to the lower side of folded or corrugated sheet 641 using tabs(also not shown) which are formed out of sheet 641 during the slittingor grooving process. The second sheet would be secured to the bottom offolded corrugated sheet 641 in a manner described in connection withsheet 656.

[0204] The result is a high-strength, fatigue-resistant and lightweightcorrugated panel or deck assembly which can be used in numerousapplications.

[0205] A corrugated panel assembly similar to FIG. 17 can be constructedas shown in connection with the assembly of FIG. 18. Folded corrugatedsheet 661 includes a plurality of fold lines 662 and a plurality of tabs663. Tabs 663 are formed from sheet 661 in a manner similar to thatdescribed in connection with tab 649, only tabs 663 include fastenerreceiving openings 664. Additionally, tabs 663 are folded down to a nearhorizontal position, rather than up to a near vertical position, asdescribed in connection with tabs 649. In the horizontal position, tab663 can be used to couple a second sheet of material 666 having fastenerreceiving openings 667 therein. Sheet 666 is positioned so that opening667 align with opening 664, and fasteners are used to secure the twosheets together. As described in connection with FIG. 17, a third sheetcan be secured to the bottom of the corrugated sheet 666, although thefigure does not show the securement tabs 664 on the bottom side of thecorrugated sheet 61.

[0206] Again, by employing a plurality of grooves or slits 668 formed inaccordance with the present invention, as above described, a corrugateddeck or panel assembly can be fabricated which is very high in strength,has good fatigue resistance and is lightweight.

[0207] FIGS. 19-22 illustrate a further embodiment of a continuouscorrugated panel or deck which can be formed using the slit sheet andmethod of the present invention. Moreover, the panel of FIGS. 19-22illustrates the strength advantages which can be obtained by reason ofthe ability to make sharp bends or folds that have significant loadcarrying capabilities. Still further, the embodiment of FIGS. 19-22illustrates the use of tabs to interlock a folded sheet into a highstrength three-dimensional structure.

[0208] Prior art techniques forming corrugated panels or decks oftenhave suffered from an inability to achieve a desired high level orpercentage of chord material to the overall panel material. Generally,the purpose of the webbing is to separate the chords with the minimalweb mass required to accomplish that task. I-beams are rolled or weldedforms that use thicker top and bottom chords relative to the connectingweb between them. The present invention enables a class of corrugatedstructures that provide for wide design flexibility in creating rigid,strong, low weight structures that can be manufactured from continuouscoils, transported in a compact coil form, and easily formed on site.The interlocking nature of this enabled embodiment avoids welding at thecorners where welding is especially subject to failure.

[0209] Sheet material 721 has been slit using the present invention andis shown in FIG. 19 in a flat state before bending or folding. As willbe seen, a plurality of substantially parallel bend lines 722 have apattern of alternating arcuate slits 723 positioned on opposite sides ofthe bend lines to define obliquely extending straps skewed in oppositedirections. Slits 723 can take the form of the slits in FIG. 6 or 9, forexample. Also formed in sheet 721 are a plurality of tabs 724 whichextend outwardly of the tongue portions of slits 723, and a plurality ofkey-hole like openings 725. Openings 725 are positioned in alignedrelation to tabs 724.

[0210] In FIG. 21A tabs 724 will be seen to extend across bend line 722from slits 723. Tabs 724 are, therefore extensions of the tongue side ofslits 723. Key hole openings 725 is a cut-out or negative tab in thetongue side of slits 723 which have a configuration dimensioned toreceive tabs 724. In order to prevent the neck of tabs 724 from beinginterfered with by the upwardly displaced face on the opposite side ofthe slits, a notch 730 is provided in the lip side of the slits 723.Thus, the entire area of 725 and 730 is cut and falls out or is removedfrom the sheet so that tabs 724 can be inserted into notches 725/730.

[0211] In FIG. 20 the flat sheet 721 of FIG. 19 has been folded into acontinuous corrugated panel or deck 726. Panel 726 includes web portions727 and chord portions 728. As will be seen in panel 726, chords 728 arein end-to-end abutting relation over the full length of the panel onboth the upper side and the lower side of the panel to providecontinuous deck or chord surfaces. This construction affords panel 726greatly enhanced strength, for example, in bending, over panels in whichall the transverse webs are not joined by chords on both the top andbottom side of the panel. The deck or panel can be further reinforced byadding a sheet of additional material (not shown) which would furtherimprove the ratio of chord material mass to the mass of the entire deckor panel for superior strength/stiffness-to-weight ratio.

[0212]FIG. 21 illustrates in greater detail the bending or foldingscheme employed for panel 726. Commencing, for example, with end flange729, web 727 a can be bent down and back at bend line 722 a down to alower side of the panel. Sheet material 721 is then bent forward at bendline 722 b and chord 728 a extends in a longitudinal. direction of thepanel parallel to flange 729. At bend line 722 c web 727 b is bent toextend up and back to bend line 722 a, at which point chord 728 b isbent forward and extends to bend line 722 b. Web 727 is then bent backat bend line 722 d to bend line 722 c. The bending continues along thelength of panel 726 so as to produce a folded corrugated panel in whichthere are a plurality of end-to-end chords on both the top and bottom ofthe panel which are separated by connecting webs. The mass of the chordmaterial in the panel to the overall panel mass is relatively high for ahigh strength-to-weight ratio.

[0213] The ability to fold a sheet 721 in sharp or crisp folds using theslitting process of the present invention allows the apexes 731 betweenthe webs 727 and chords 728 to be relatively sharp and to be positionedin close, abutting relation. As illustrated, the panel of FIGS. 19-21has webs and chords of equal length creating equilateral triangles inwhich each apex is about 120 degrees. As will be understood, many othercorrugation geometries are equally possible.

[0214] While there are numerous ways in which folded panel 726 can besecured in a three-dimensional configuration, a preferred method is toemploy tabs 724 and mating keyhole openings 725 cut into sheet 721during formation of the bending slits.

[0215] Tabs 724 a, for example, are provided by laser or water jetcutting of the tabs to extend outwardly of slit tongues from flange 729into web 727 a. When web 727 a is bent downwardly and rearwardly to bendline 722 b, tabs 724 a remain in the horizontal plane of flange 729. Asbest seen in FIG. 21A, a mating opening 725 cut into chord 728 b andaligned with tab 724 a will allow tab 724 a to be positioned in opening725. If each tab 724 has an enlarged head or end 734, the tabs will lockor be captured by their mating openings 725, much as a jigsaw piece cancapture or interlock with an adjacent piece. This interlocking resistsseparation of the tabs from the mating openings in the top and bottomplanes of the panel. The tabs and openings do not need to be, andpreferably are not, dimensioned to produce an interference fit.

[0216] Interlocking of tabs 724 and openings 725 also occurs along thebottom side of panel 726, and the result is securement of the foldedpanel in the form as shown in FIG. 20, even without additionalsecurement techniques, such as adhesives, welding, brazing or the like,which optionally also can be used.

[0217] In FIG. 22, the sheet slitting and bending process of FIGS. 19-21is schematically shown as applied to the formation of a cylindricalmember 741. Again, webs 742 and chords 743 are formed about bend linesand the locations of the bend lines selected so that the chords on theinner radius 744 are shorter in their length than the chords on theouter radius 746 of cylinder 741. Tabs and mating opening may be used tolock the chords and webs in the desired configuration, depending on thethickness of the material and the radii of cylinder 741. The resultingcylindrical structure can be used, for example, as a lightweight,high-strength column or post.

[0218] In most embodiments of the present invention, and particularlythose in which the sheet of material has a substantial thickness,commencement of bending will automatically cause the tongue or tabportion of the slit to begin to slide in the correct direction againstthe face on the opposite side of the slit. When the sheet material isrelatively thin and the kerf of the slit is small or zero, however thetab portions of the slit sheet occasionally will move in the wrongdirection and thereby effect the precision of the bend. In order toremedy this problem, it is possible for the tongue portion of the slitto be biased in a direction producing predictable proper bending. Thissolution is shown in FIGS. 23 and 24A.

[0219] A sheet of material 681 is formed for bending about a plane ofbend line 682 using the design and sheet slitting technique of thepresent invention. Arcuate slits 683 are formed which define tongues 684that will slide along opposing faces during bending of the sheet aboutbend line 682.

[0220] In FIG. 23a, sheet of material 681 can be seen as it is beingbent in a downward direction, as indicated by arrows 687, about bendline 682. Because tongues 684 are downwardly displaced, the lower edgesor corners 688 of lips 689 will tuck up and engage faces 690 of tonguesin a manner which will produce sliding of edges 688 along faces 690. Theedges 688 on each side of bend line 682 will be displaced upwardly toslide on the downwardly pre-set tongues 684 so that bending about bendline 682 predictably produces sliding of the edges along the faces ofthe tongues in the desired direction during the bending process.

[0221] When sheet 681 is formed for bending using, for example, astamping process in which a knife forms slit 683, the stamping die canalso plastically deform tongues 684 in a downward direction on side ofthe bend line. Predictable sliding of edge 688 along face 690 in theproper direction will occur during bending so that the actual fulcrumson opposite sides of the bend line will produce precise bending alongthe virtual fulcrum aligned with bend line 682. The displaced tonguesalso will cue an operator as to the proper direction for bending.

[0222] While many applications of the present invention will call for 90degree bends, some will call for bends at other angles. The apparatusand method of the present invention can accommodate such bends whilestill maintaining the advantages of full edge-to-face contact. In FIG.24, a bend of about 75 degrees is illustrated.

[0223] As shown, a sheet of material 691 is formed with a slit 692 whichis cut at an angle of a of about 75 degrees to the plane of sheet 691.(A corresponding slit on the other side of bend line 693 also cut at 75degrees but skewed in the opposite direction is not shown for simplicityof illustration.) Upon bending downwardly, lower edge 694 of lip 695tucks onto and slides up face 696 of tongue 697. Once the bend reaches105 degrees, or the complimentary angle to slit angle α, the lowersurface 698 of the sheet proximate edge 694 will be coplanar with andevenly supported on face 696 of the tongue.

[0224] Today most commercial laser cutters with power capable of cuttingboth plastics and metals are sheet fed. There is, however, supply-rollfed laser cutting equipment commercially available, but such equipmentthat exists today does not roll the cut material back into a coil. Thus,reel-to-reel laser cutting equipment is not in use or commerciallyavailable.

[0225] The advantage of roll fed cutting combined with a coil mechanism,in the context of the present invention, is that very large or verycomplex, information-rich structures can be designed in CAD, cut, andthen these pre-engineered structures can be recoiled into a compactform. Once in the coiled, compact form, they may be transported moreconveniently, for example, on a flat-bed truck or rail car or launchedinto outer space. Upon arrival at the location of use, the material isuncoiled and bent or folded along the bend lines dictated andstructurally supported by the arcuate slits and oblique straps cut intothe metallic or plastic sheet.

[0226] The sheet slitting or grooving apparatus and method of thepresent invention can be incorporated into a reel-to-reel process in atleast three ways. Widely available throughout industry are flat-bedlaser cutters of many types. The first approach uses a coil on one endof a flat-bed laser cutter, the laser cutter in the middle and a windingroll for reforming a coil of partially cut material. The material isadvanced through the system by hand and pin or edge-notch registrationfeatures are cut into the flattened sheet. The sheet is aligned in bothX and Y axis by physically docking the cut features with a jig attachedto the laser cutter bed. In this way, piece-wise advancement can occurincluding the alignment of slit-assisted bending features of the presentinvention. The novelty is in the combination of the registration systemwith the uncoiling and coiling of material-together with the applicationof cut bend-producing features of the present invention that enablelow-force, precisely located, high strength bent or folded structures.

[0227] A second approach is to advance a coil through a laser cutterusing the well-known technique of a power unwind, stop, cut and powerrewind.

[0228] A third approach is shown in FIG. 25. It employs a smooth,continuous web transport, with both unwind and rewind. Sheet material701 is unwound from supply coil 702, and the motion and/or optics of theCNC cutter 703 is controlled to compensate for the rolling frame ofmaterial 701. CNC cutter 703 can be a laser cutter or a water jet cutterformed and controlled to cut the desired slit patterns into sheet 701.After cutting, sheet 701 is wound onto coil 704.

[0229] Since coiled sheet stock often will have a coil-set curl, the useof a leveling step or leveling apparatus 706 after unwinding coil 702 isan option. Sheet stock 701 can be driven through the processing line bypinch rollers 707 and drive motors at coils 702 and 704 and additionallyat roller 710.

[0230] One reason that reel-to-reel processing has not been previouslyused is that the edges or contours of the cut-out features tend tointerlock and snag as successive layers are would up on coil 704,particularly when the low-force slit-assisted bend features of thepresent invention enable a foldable tab or flap. The very act ofrecoiling material 701 will tend to make the cut tabs or flaps extendtangentially to the winding coil. Two methods can be used to addressthis issue. One is the use of thin, easily removed hang-tabs incombination with rewinding a coil of metal and other rigid materialsthat have these low-force folding features of the present invention thattend to extend from the rewound coil tangentially. A second method isshown in FIG. 25, namely, to co-wind a polymer web 708 onto coil 704.Web 708 should be tough and not easily punctured, yet thin in gage.Polypropylene and polyethylene are but two useful examples.

[0231] One technique for increasing the throughput of reel-to-reelprocessing systems is the use of laser cutter 703 having multiple laserbeams for cutting the slit-assisted, low-force bend features of thepresent invention. Foldable box beams, such as is shown in FIG. 12, needseveral bend-assisting arcuate slits that are arranged parallel to thecoil's winding direction, about a desired bend line. Multiple fiberlasers, for example, that are linked together mechanically and whosemotion controller is a single, joined, mechanical system, with a singlemotion controller, can produce all of the parallel bends at the sametime, while other lasers with independent motion actuation systems andmotion controllers can produce all other cut features, such as thenotched edges.

[0232] The methods and apparatus of the three reel-to-reel processingsystems described above, combined with the low bending-force, highstrength bend features of the present invention, enable a class ofproducts, from beams, to ladders, to building stud and joist systems, tobe formed, coiled, subsequently uncoiled and folded into deterministicdimensions of impressive structural integrity, when and where they areneeded after compact storage or transport in coiled form. This techniquehas applications in space, in the military, in commercial andresidential construction and many other industries where the costs andeffort of getting materials to a site are prohibitively expensive anddifficult when parts are already in an assembled state.

[0233] Optionally the reel-to-reel processing line of FIG. 25 can alsoinclude a pair of hard-tooled die cutters 709. Using male and femalestamping shapes to stamp out the arcuate slits and drop-out features,the die cutters also can be plates and apply incremental materialhandling techniques, but most preferably, they are hard tooled rotarydies 709.

[0234] The advantage of the CNC cutting approach to fabricatingcoil-wound engineered folding structures is that non-repetitive featuresare easily programmed into the cutting process. The advantage of thehard tooled stamping or rotary die cutting approach, whetherintermittent or continuous, is that repetitive features, especially thearcuate slits, can be efficiently made.

[0235] The greatest benefits of maximum throughput and flexibility maybe advisable using CNC cutting in combination with the hard-tooledstamping/die cutting to yield an inline system with both forming stepslocated between the unwinding and rewinding steps of the process. In thecombined system, such as shown in FIG. 25, each forming tool operates toits own advantage.

[0236]FIG. 25 illustrates a method can be used to form three-dimensionalstructures for use particularly at locations remote of the location atwhich the structure is slit and/or partially assembled prior to bending.One application is of particular interest is the fabrication ofthree-dimensional structures in outer space. Currently such structuresare assembled in outer space from three-dimensional modules; theygenerally are not actually fabricated in outer space. The problem withspace assembly is that the modules require an undesirable amount ofvolume in the payload of orbital space vehicles. Heretofore, one problemwith fabrication in outer space has been that the tools required to formhigh-strength, three-dimensional structures have been prohibitivelylarge and bulky. Another problem with assembly in space can beassociated with a high part count and high fastener count. On the onehand, bulky near complete modules have been launched and fastenedtogether. On the other hand, heretofore, dense packing of unassembledmodules has resulted in a high part count and high fastener count.

[0237] In FIG. 26, a coil 339 of sheet material 341 is shown which hasbeen designed and provided with slits or grooved on two bend lines 345.Sheet 341 is also formed with openings 346 and tabs 348 periodicallypositioned proximate opposed sheet edges. As will be seen, slits 343 mayadvantageously take the configuration as shown in FIG. 6. As will beappreciated, coil 339 is a highly compact configuration for thetransport of sheet material. Sheet 341 can be formed with slits 243,openings 346 and tabs 348, as well as other desired structural features,at an earth-bound shop having unlimited fabrication equipment, forexample, using the reel-to-reel processing line of FIG. 25. The coiledsheet is next transported by a space vehicle to an outer space location.Sheet 341 can then be unrolled from coil 339, and either, while beingunrolled, or thereafter, the sheet can be fabricated, using hand toolsor moderately powered tools, into a three-dimensional structure. Suchfabrication is accomplished by bending the sheet along bend lines 345and by bending tabs 348 into openings 346 so as to lock the sheet in athree-dimensional structure such as a triangular beam 350, as shown atthe right-hand side of FIG. 26.

[0238] As shown in FIG. 26, structure 350 is an elongated beam with atriangular cross section can, in turn, be coupled to other structures toproduce complex three-dimensional space structures and habitats. Whenthe sheet bending slit configuration of the present invention isemployed, each of the bends produced at the pattern of slits 343 willpreferably include the edge-to-face support of the sheet material whichwill make the bends capable of withstanding substantial loading.Obviously, other beam and structural configurations, such as the boxbeam of FIGS. 13 and 14, the deck of FIG. 20 or the column of FIG. 22,can be produced by folding along bend lines having slits of the typedescribed above.

[0239] Moreover, using the slitting and grooving method and apparatus ofthe present invention ensures the precise positioning of the opposededges of the sheet 341 and openings 346 and tabs 348 so as to enableclosure of structure 350. If the structure to be formed needs to befluid-tight and slitting is employed, the bends produced by slits 343can be adhesively or otherwise filled, for example, by welding orbrazing. It is also possible to provide numerous other closureconfigurations or fastening schemes, including welding along theabutting edges of sheet 341 and overlapping of an edge of the sheet witha side wall and the use of tabs and/or fasteners.

[0240] Another form of box beam which illustrates the flexibility of theapparatus and process of the present invention is shown in FIGS.27A-27G, namely a cross or self-braced box beam.

[0241] Sheet of material 801 is shown in FIG. 27A as being slit alongbend lines 802 and 803. Additionally, a plurality of transverse slits804 are provided which will be used to provide beam cross-bracing sheetportions 806. Bending of sheet 801 into a cross-braced box beam 8079FIG. 27G) is shown in the sequence of FIGS. 27B-27G.

[0242] First, the side of the sheet having the cross-bracing sheetportions 806 can be bent to the position of FIG. 27B. Next, the sheet isbent along bend lines 803 to produce the cross braces 806 of FIG. 27C.Sheet 801 is then bent about bend line 802 a to the position of FIG.27D. The sheet is bent about bend lines 802 b and 802 c in FIGS. 27E and27F, and finally side flange 805 is bent up and the sheet bent aboutbend line 802 d to produce beam 807 of FIG. 27G. Fasteners can be placedin openings 808 and 809 (which are formed in aligned registered relationin sheet 801), such as rivets or screws, can be used to secure sideflange 805 to the remainder of the box beam to produce a structure whichwill not bend or unfold. Beam 807 will be seen to trap or capture at itscenter an X-shaped cross-beam array extending along the beam to give itsubstantially enhanced strength. An extremely high-strength to weight,internally braced box beam, therefore, can be designed and formed from asingle sheet of material using the process of the present invention.

[0243] As an optional step that can be added to many differentstructures formed using the apparatus and method of the presentinvention, protective corners or shin guards 810 (FIG. 27G) can beattached over bent corners 802 to effect a smooth and/or decorativecorner treatment. Thus, L-shaped shin guard 810 can be added to beam807, as indicated by arrows 820, and secured in place by, for example,adhesives or fasteners. Shin guards 810 can be metallic plastic or evenreflective to produce decorative effects, as well as to provide impactprotection, to smooth and/or to seal or pot the corner bends. Shin guard810 could even encircle the beam or other three-dimensional structure.Attached shin guards can assist in load transfer across the bends.

[0244] In the cross braced box beam 807 of FIGS. 27A-27G, the crossbracing sheet portions 806 are bent to an “X” configuration and thencaptured or trapped within the folded beam to provide internal bracing.Another approach to the bracing of structures having adjacent walls indifferent planes is to employ swing-out sheet portions.

[0245] FIGS. 34A-34E illustrate the use of swing-out bracing in anotherbox beam that also has a pattern of weight-saving cutouts. In FIG. 34A,sheet 811 has been slit using the present invention with a plurality ofbend lines 812. Sheet 811 has further been cut or stamped with cutoutsor weight saving openings 813. Additionally, in order to provide bracingof the folded walls of the beam, a plurality of swing-out sheet portions814 have been provided which can be bent around bend lines 815.

[0246] In FIG. 34B swing-outs 814 have been folded or swung out of theplane of sheet 811 around bend lines 815, while in FIG. 34C, the outsideedges 816 of the sheet have been bent to a vertical orientation aroundbend lines 812. In FIG. 34D one side wall portion 817 of sheet 811 hasbeen bent again around a bend 812, and in FIG. 34E the other side wallportion 817 has been bent around another bend line 812 to complete thebox beam 818.

[0247] The last bending step, namely, bending from the configuration ofFIG. 34D to that of 34E, causes edge portions 816 to overlap and causesswing-outs 814 to overlap. Both edges 816 and swing-out 814 can beprovided with fastener-receiving openings 819 which will become alignedor superimposed as the beam is folded to the FIG. 34E condition byreason of the high precision or accuracy possible when employing theedge-to-face bending technique of the present invention. Thus,fasteners, such as rivets or screws, not shown, can be inserted intoopening 819 to secure edges 816 together against unfolding of beam 819,and to secure swing-outs 814 together to provide bracing betweenmutually perpendicular walls of the beam, as well as bracing across thebeam. As will be apparent, the number of bracing swing-outs can beincreased from that shown in the illustrated embodiment, and the use ofswing-outs to brace adjacent walls in different planes has applicationto many structures other than box-beams.

[0248] Turning now to FIGS. 29 and 30, the advantages of low-force sheetbending enabled by the present invention can be illustrated. In FIG. 29,a sheet of material 841 is shown which has a plurality of arcuate slits842 formed along bend lines in a manner above described. Formation ofbox 843 from sheet 841 can be easily accomplished using low-forcetechniques.

[0249] Sheet 843 can be placed over opening 844 in die 846 and the foursides 847 of the box simultaneously bent to upright positions. Anactuator driven plunger 848 can be employed or a vacuum source coupledto apply a vacuum to die 846 through conduit 849 used. Little or noclamping of sheet 841 to die 846 is required; only positioning of sheet841 so that the bend lines are in mating relationship with opening 844in the die. This can be accomplished, for example, by providing indexingpins (not shown) on the top surface of the die proximate the corners ofopening 844. The indexing pins would engage sheet 844 at the apexesbetween sides 847 of sheet 841.

[0250] Depending upon the material being bent and its thickness, anegative pressure at conduit 849 will be sufficient to pull sheet 841down into the die and thereby bend sides 847 up, or for thicker sheetsand stronger materials, plunger 848 may also be used or required toeffect bending.

[0251] Box 843 can be used, for example, as RFI shields for smallcircuit boards, such as the ones commonly found in hand-held cellphones, have been made by the prior art technique of progressive diestamping. The advantage of progressive die stamping is that sufficientprecision can be achieved and it is suitable to low cost, massproduction. However, with the rapid change in products that face thismarket, new shield designs require that the hard tooling be frequentlyreplaced. This is especially problematic at the development end of theproduct life cycle where many changes occur before the final design ischosen. Another difficulty with relying on hard tooling is that theramp-up to full production must wait until the hard tooling isavailable. This can be as much as eight weeks, which is very expensivein a market with rapid design changes and short product life. Yetanother problem with the progressive die stamping has to do withaccessibility to the underlying components for diagnostics or repair. Ifa significant fraction of a chip batch is faulty and may need repair, atwo-piece RFI shield unit is employed with a low profile fence, solderedto the circuit and a “shoe box lid” covering it with an interferencefit. This disadvantage is that the fence below take some horizontal“real estate” away from the circuit board and two pieces are always moreexpensive to manufacture than one. Another prior art solution toaccessibility is the method of using a row of circular perforations inthe shield lid that can be severed to allow an area of the lid to behinged upward along one side. This perforated door approach crates thepossibility of some RFI leakage and it is difficult to cut and resealthe lid.

[0252] Box 843 of FIG. 29 shows a solution to the aforementionedproblems using the techniques of the present invention. The RFI shieldsmanufactured using arcuate slit assisted bending methods can be rapidlyprototyped without hard tooling using a CAD system for design and a CNCcutting process such as a laser cutter. Folding to the required shapecan be readily accomplished by hand tools or the fabrication equipmentof FIG. 29.

[0253] The ramp-up to full production can be accomplished immediately bylaser cutting the initial production volumes required to enter themarker. Lower cost stamping tools to stamp out the biased tongue-tabsneeded for the geometry disclosed can be fabricated during the ramp-upphase that initially is supplied by a CNC cut solution. In this way, thecost of design, ramp-up, and production can be lowered relative to thecurrent practice of waiting for progressive cavity dies to bemanufactured.

[0254] Another advantage of the present invention is the built-in accessdoor for servicing the parts within. By severing the straps defined byslits 842 around three sides of shield 843, and having previouslysoldered edges 850 of the low profile rectangular box 843 to the circuitboard, the panel 840 of box 843 can be hinged 90 degrees to allow fortemporary service access. When repairs are complete, the lid or panel840 can be closed again and re-soldered at the corners. Most metalalloys suitable for RFI shielding will allow for eight or more accessesin this manner before the hinged straps fail.

[0255] In FIG. 30 a series of steps is shown in which a sheet 861, whichhas been slit according to the present invention, can be popped up intoa box using a pneumatic bladder or vacuum grippers.

[0256] Sheet 861 is shown in a flat form at the left side of thesequence of FIG. 30. Sheet 861 is, in fact, two identical sheets whichhave been coupled together at bend lines 826 at the outer edges of sides863 of the sheets, as will become apparent as the box is formed. Sheet861 can be transported in the substantially flat state shown on the leftend of the sequence and then, at the use site, popped up to thethree-dimensional box 865 shown at the right hand side of the sequence.This in-the-field formation of box 865 can be easily accomplished usingpneumatics or hydraulics because the bending of sheet 861 requires onlythe minimal force necessary to bend the oblique bending straps.

[0257] One bending technique would be to employ suction or vacuumgrippers 864 which are moved, as indicated by arrows 866, down intocontact with a planar central sheet portion 867 of sheet 861. A vacuumis applied to suction grippers 864 and then the grippers are movedapart, as indicated by arrows 868 until box 865 is fully distended, asshown at the right hand side of FIG. 30.

[0258] Another approach is to insert an expansible bladder 869 into theslightly distended box, as shown by arrow 871. Such insertion can beaccomplished before transportation or in the field. Bladder 869 is theninflated pneumatically or hydraulically and the box gradually distendedor bent up to the condition shown at the right hand side of FIG. 30.

[0259] Box 865 can be secured in the configuration shown at the righthand side of FIG. 30 by, for example, welding, brazing or adhesivelysecuring side panels 863 at corners 872.

[0260] A further advantage of the high precision bending or foldingprocess of the present invention is that geometric information may beembedded in the planar material at the same time that the low-force,high precision bending structures are fabricated. This information maybe accurately and predictably communicated into an anticipated 3Dspatial relationship at very low cost.

[0261] In the past, symbols and geometric conventions have been used toconvey information about the assembly of structures. One aspect of thepresent invention is that the bending or folding instructions may beimparted to the flat parts of the sheet material at the same time thatthey are formed with bending slits or grooves.

[0262] Alternatively, folding instructions may be imparted to the flatparts through a secondary process such as printing, labeling, ortagging. Additionally, information may be embedded in the flat form thatis intended to instruct the assembly process of similarly precision-bentstructures or the adjoining of parts from non-folded prior art andfuture art fabrication methods.

[0263] For example, a continuous pre-engineered wall structured may beformed from a single sheet of material that is folded into top andbottom joists with folded-up studs. All anticipated windows, doors andelectrical boxes can be embedded as physical geometric information inthe flat part for subsequent folding and assembly into the building. Aconvention may be established that a round hole in the structure isindicative of electrical conduit that will later be threaded through thehole. A round-cornered square hole may be indicative of hot water copperpipe that should be passed through the wall. In this way, the feature isnot only located in the flat part, but it is very accurately translatedinto correct 3D relationship, and finally, such conventions communicateto trades people, who are not involved with the structural erection ofthe building, where their activities intersect with the structure.Moreover, communication of such information anticipates the tradespeople's activity so that they do not have to modify and repair thestructure as they thread their infrastructure through the building.

[0264] FIGS. 32A-32E illustrate an embodiment of a stud wall which canbe folded out of a single sheet of material using the sheet bendingmethod of the present invention. In FIGS. 32A-32E no attempt has beenmade to illustrate openings or the like which are precisely positionedand shaped to communicate information, but such data can be preciselylocated during the sheet slitting process. It should also be noted thatthe folded sheet of FIG. 32E can either be a stud wall with studs joinedto joists or a ladder with rungs joined to side rails

[0265] Turning to FIG. 32A, sheet of material 901 has been slit along aplurality of bend lines to enable formation of a stud wall or ladderstructure. The slits are formed and positioned as taught herein.

[0266] In FIG. 32B the side wall portions 902 of eventual studs orladder rung 903 have been folded up along bend lines 904 from flat sheet901. The next step is to fold up an additional end wall or step portion906 along bend line 907, as shown in FIG. 32C. In FIG. 32D the joists orladder rails 908 are folded up along bend line 909, and finally thejoists/rails 908 are folded again along bend line 911 in FIG. 32E. Thislast fold causes openings 912 in joist/rails 908 to be superimposed inaligned or registered relation to openings 913 (FIG. 32D) in side walls902 of the studs/rungs 903. Fasteners, such as rivets or screws can beused to secure the joist/rails 908 to the studs/rungs 903 and therebysecure the assembly in a load bearing three-dimensional form 914.

[0267] When used as a ladder, rails 908 are vertically extending whilerungs 903 are horizontal. When used as a stud wall, joists 908 arehorizontal and studs 903 are vertically extending. As will beappreciated, the rungs/studs and rails/joists also would be scaledappropriately to the application.

[0268] As set forth above, most uses of the slitting process and slitsheets of the present invention will require that a plurality of slitsbe placed in offset relation along opposite sides of the desired bendline. This approach will produce the most accurate or precise sheetstock bends since three will be two opposed and spaced apart actualfulcrums that precisely cause the position of the virtual fulcrum to bebetween the actual fulcrums on the desired bend line.

[0269] While there is a very minor loss of bending precision, thetechnique of the present invention can also be employed using a singleslit and bending straps configured to produce bending of the sheet ofmaterial along a bend line, while edge-to-face engagement of the sheetportions across the slit occurs. This single slit bending is illustratedin FIGS. 35 and 36.

[0270] In FIG. 35 a sheet of material 941 is shown which has been slitfor bending into a wheel roller housing, generally designated 942, asshown in FIG. 36. Sheet 941 includes a slit 943 for bending of ear 944about bend line 946. As will be seen, there is no slit on the side ofbend line 946 opposed to slit 943. Nevertheless, ear 944 includes twoshoulders 947 that define bending straps 948 with arcuate end portion949 of slit 943. It also will be apparent that the central axes 951 ofbending straps 948 are oblique to bending line 946 in oppositely skeweddirections.

[0271] When ear 944 is bent into the page for FIG. 35, oblique straps948 will bend and twist and at the same time pull or draw lip 952 on theear side of slit 943 up into engagement with the face of tongue 953 onthe body side of the slit. Thus, sliding edge-to-face engagement againis produced by reason of oblique bending straps 948, correctly scaledand shaped.

[0272] Sheet 941 has other examples of arcuate bending slits whichcombine with partial opposed sits or edges of the sheet to providebending straps that will produce edge-to-face bending. For bending line956, for example, slit 943 a is opposed at one end by a partial slit 957having an arcuate end 958 that combines with arcuate end 949 a to definean oblique bending strap 948 a. At the opposite end of slit 943 a anarcuate edge portion 959 combines with arcuate slit end 949 a to defineanother oppositely skewed strap 948 a.

[0273] The result of the configuration of straps 948 a is edge-to-facebending about bend line 956.

[0274] Slit 943 b is formed as a mirror image of slit 943 a with anarcuate edge and partial slit cooperating to define oblique bendingstraps 948 b. Similarly, slit 943 c cooperates with an edge and partialslit to define oblique bending straps 948 c that ensure edge-to-facebending. Finally, slit 943 d cooperated with slit portions 960 to defineobliquely oriented bending straps 948 d.

[0275] The single slit embodiment of the present apparatus and method asillustrated in FIG. 35 is somewhat less precise in the positioning ofthe bend on desired bending line, but the loss of accuracy is notsignificant for many applications. In the structure illustrated in FIG.36, an axle 961 for roller 962 passes through openings 963, 964 and 965(FIG. 35) which must come into alignment when sheet 941 is bent into thethree-dimensional housing 942 of FIG. 36. The single slit embodiment,therefore, will produce bends which are still sufficiently precise as toenable alignment of openings 963, 964 and 965 to within a fewthousandths of an inch for insertion of axle 961 therethrough.

[0276] In FIG. 37, bend line termination or edge-effects related to theslitting process and apparatus of the present invention are illustrated.A sheet of material 971 is shown with five bend lines 972-976. Slits 981are formed in the sheet along the bend lines as described above. Theedge 982 of sheet 971 should be considered when designing the slitlayout because it can influence the positioning of the slits.

[0277] On bend line 972 slits 981 were given a length and spacing suchthat a partial slit 981 a opoens to edge 982 of the sheet of material.This is an acceptable bend line termination strategy. On bend line 973,partial slit 981 b again opens to edge 982, but the partial slit 981 bis long enough to include arcuate end 983 so that a bending strap 984 ispresent to oppose bending strap 986. Slit 987 can also be seen to have arectangular opening 988 extending across the slit. Opening 988 is in thecentral portion of slit 987 and therefore will not significantlyinfluence bending straps 984 or 986, nor will it effect edge-to-facebending.

[0278] On bend line 974, slit 981 c has an arcuate end 989 which defineswith sloping edge portion 991 an oblique bending strap 992. A similargeometry is shown for slit 981 d and edge portion 993. The use of anedge of a sheet to partially define a bending strap is also employed inconnection with the slits of FIG. 35, as above described.

[0279] Finally, on bend line 976 arcuate edge portion 994 cooperateswith arcuate end 996 of slit 981 e to define strap 997. Thus, the edgeportion 994 requires a slit layout which inverts slit 981 e from theorientation of slit 981 d and illustrates that the finite nature of theslits requires that edge effects be considered when laying out theslits. In most cases, slit length can be slightly adjusted to producethe desired bend line termination or edge effect.

[0280] In a further aspect of the present invention, as schematicallyshown in FIG. 31, a method is provided for forming three-dimensionalstructures. The first step is designing the three-dimensional structure.This involves an initial sub-step 370 a of imagining the design. Onceconceptualized, designing will often, but not necessarily, proceed witha step 370 b or 370 c in which CAD or computer implemented designingtakes place. The step 371 of selecting a sheet of material and itsthickness optionally can occur before or during CAD design steps 370 bor 370 c.

[0281] As can be seen in FIG. 31, CAD design steps 370 b and 370 c caninclude various alternative sub-steps. Thus, a common approach issub-step 370 b ₁ in which the conceptual design is built in 3-D CAD andthen flattened. Alternatively at step 370 b ₂, the design can be builtup by successively bending sheet flanges or portions. One can alsodesign in 2-D and declare or locate the bend lines, which is sub-step370 b ₃. Placement of the proper or best-designed slits or grooves ofthe present invention can be done through software, at step 370 b ₄ ormanually at the step 370 b ₅.

[0282] The design process of the present invention can also be basedupon a selection, usually by computer or a CAD software program, atsub-step 370 c ₁ among a plurality of stored designs and/or parts. TheCAD system can then, at sub-step 370 c ₂, modify the selected part toachieve the new or desired design, if modification is required. Finally,at sub-step 370 c ₃ the part is unfolded by the software into a flatstate.

[0283] Once designed, the next step is a slitting or grooving step 373,preferably by employing a CNC controller to drive a sheet stock slittingapparatus. Thus, at sub-step 373 a data, representing the flat part andthe designed slits or grooves, are transferred from the CAD or CAMsystems to a CNC controller. The controller then controls slitting andother formation steps for the cutting and fabricating equipment. Atsub-step 373 b, therefore, the flat part is formed using additive(molding, casting, stereo lithography) or subtractive (slitting,cutting) or severing (punching, stamping, die cutting) fabricationtechnique.

[0284] Optionally, the formed flat sheet can also undergo such steps assurface treatment 373 c, affixation of components 373 d, testing 373 e ₄and storage 373 f, usually in a flat or coiled condition.

[0285] Often a transportation step 375 will occur before the sheetmaterial is bent or folded at step 377. The slit sheet stock is mostefficiently transported from the fabrication site to a remote bendingand assembly site in a flat or coiled condition.

[0286] Bending or folding 377 is precise and low-force. For moststructures bending occurs along a plurality of bend lines and oftencontinues until two portions of the sheet are abutting, at which pointthey can be coupled together at the abutting portions of the sheet toproduce a rigid load-bearing three-dimensional structure at step 379.Optionally, the structure can be secured in a three-dimensional, loadbearing configuration by an enveloping step, which couples the foldedpart together by encircling it.

[0287] Envelopment can be used for at least three strategies. In thepresent invention, the angle of a fold is not informed by the geometryof slits that form it. (Notwithstanding the technique of using a slittilt angle to affect maximum contact area of edge to face engagement fora particular angle of folding, as shown in FIG. 24.) The angle of eachfold is generally dictated by at least three interlocking planes. Insome cases there is no opportunity to interlock three orthogonallyindependent planes, so an alternate method of defining a restrictedrotational angle is needed. One method is to fold the structure againsta reference structure of known angular relationship and lock theangle(s) into place by methods of adhesive(s), brazing, welding,soldering, or attaching structural shin guards to the inside or outsideof the fold. Another method is to use an interior structure of definedangular form and bend the structure around it, that is to envelop theinterior structure. This second method is referred to in the design andfabrication process diagram of FIG. 31, by reference numeral 376 a,b. Inthis embodiment of envelopment, the interior part may be left in place(376 b) or in some cases, it aids in the folding process only and issubsequently removed (376 a).

[0288] Another use for envelopment is to capture, which is the processof docking together a folded sheet structure of the present inventionwith a functional part that may or may not be formed by the presentinvention, by enfolding or enveloping parts or modules within anotherstructure. For example, FIG. 16 illustrates but one of many “capture”opportunities of the enabling feature of envelopment in the presentinvention 376 b. Thus, column 631 is enveloped by folded sheet 611.

[0289] Yet another class of envelopment can occur, when connections aremade between two or more modules of folded plate construction of thepresent invention, or between two or more components that include atleast one structure of folded plate construction of the presentinvention. The three-dimensional positional accuracy of features formedin a planar material of the present invention, combined with theenveloping nature of the closure or coupling process, enable a method ofjoining together multiple pieces with a very high rate of success thatdoes not require secondary cut and fit adjustments. This is distinctfrom the capacity of the present invention to align fastening features,such as holes, tabs and slots. It is a method of joining together bywrapping around.

[0290] The process of the present invention can also include aniterative step 380. The ability to create low-cost three-dimensionalparts using the present method affords the designer the practical luxuryof being able to tweak the design before settling on a productiondesign.

[0291] The slit-base bending method and apparatus of the presentinvention are capable of highly precise bending tolerances. The originalslits can be laid out with extreme precision using a CNC machine tocontrol, for example, a laser, or water jet cutter, stamping or punchingdie, and the bends which are produced will be located with ±0.005 inchestolerance while working with macroscopic parts. This is at least as goodor better than can be achieved using a press brake and a highly skilledoperator. One additional advantage of using a stamping die is that thedie can be wedge-shaped to compress the slit transversely or in the kerfwidth direction. This will compress the sheet material locally at theslit for better fatigue resistance. Such transverse compression alsomust be considered when designing a kerf width to produce edge-to-facecontact during bending. It also is possible to follow laser or water jetcutting by a transverse compression of the slit with a wedge shapedstamping die to enhance fatigue resistance.

[0292] Moreover, when using the bending scheme of the present invention,the tolerances errors do not accumulate, as would be the case for apress brake. Alternatively, the slits or grooves can be cast or moldedinto a sheet of material or cast three-dimensional member having asheet-like extension or flap that needed to be folded. While workingwith materials of near microscopic or microscopic dimensions, otherforming methods commonly used in the field of microelectronics and MEMSsuch a e-beam lithography and etching may be used to effect the requiredgeometry of the present invention with extreme accuracy.

[0293] Rather than manipulating a laser beam (or sheet of material) toproduce curved grooves or slits, such beams can also be optionallycontrolled or shaped to the desired configuration and used to cutgrooves or slits without beam movement. The power requirements presentlymake this most feasible for light guage sheets of metals or plastics.

[0294] Fabrication techniques in the method of the present inventionalso may include steps such as deburring the slits or grooves, solventetching, anodizing, treating to prevent surface corrosion, and applyingcompliant coatings, such as paints, polymers, and various caulkingcompounds.

[0295] From the above description it also will be understood thatanother aspect of the method for precision bending of a sheet materialof the present invention includes the step of forming a plurality oflongitudinally extending slits or grooves in axially spaced relation ina direction extending along and proximate a bend line to define bendingstrap webs between pairs of longitudinally adjacent slits. In oneembodiment, the longitudinally extending slits are each formed bylongitudinally extending slit segments that are connected by at leastone transversely extending slit segment. In a second embodiment, theslits or grooves are arcs or have end portions which diverge away fromthe bend line to define bending straps, which are preferably oblique tothe bend line and increasing in width. In both embodiments, the strapscan produce bending about virtual fulcrums with resulting edge-to-faceengagement of the sheet material on opposite sides of the slits. Thenumber and length of the bending straps webs and slits or grooves alsocan be varied considerably within the scope of the present invention.The width or cross sectional area of the bending straps and thetransverse divergence of the straps also can be varied independently ofthe transverse spacing between slits. An additional step of the presentmethod is bending of the sheet of material substantially along the bendline across the bending web.

[0296] The method of the present invention can be applied to varioustypes of sheet stock. It is particularly well suited for use with metalsheet stock, such as aluminum or steel, which can have substantialthickness and a variety of tempers (for example, 2 inch carbon steel,6061 aluminum with a T6 temper, some ceramics and composites). Certaintypes of plastic or polymer sheets and plastically deformable compositesheets, however, also may be suitable for bending using the method ofthe present invention. The properties of these materials are relative toa given temperature and fluctuations in temperature may be required tomake a particular material suitable in the context of the presentinvention. The present method and resulting sheets of slit material areparticularly well suited for precision bending at locations remote ofthe slitter or groover. Moreover, the bends may be produced preciselywithout using a press brake.

[0297] Sheet stock can also be press brake bent, as well as slit orgrooved, for later bending by the fabricator. This allows the sheetstock to be shipped in a flat or nested configuration for bending at aremote manufacturing site to complete the enclosure. Press brake bendscan be stronger than unreinforced slit bends so that a combination ofthe two can be used to enhance the strength of the resulting product,with the press brake bends being positioned, for example, along thesheet edges. The slit or grooved bends can only be partially bent toopen outwardly slightly so that such sheets can still be nested forshipping.

[0298] The bent product has overlapping edge-to-face engagement andsupport. This enhances the ability of the product to withstand loadingfrom various directions without significant stressing of the bendingstraps. If further strength is required, or for cosmetic reasons, thebent sheet material can also be reinforced, for example by welding orotherwise attaching a shin guard or bent sheet along the bend line. Itshould be noted that one of the advantages of forming slits withessentially zero kerf, is that the bent sheet has fewer openingstherethrough along the bend line. Thus, welding or filling along thebend line for cosmetic reasons is less likely to be required.

[0299] It will be noted that while straight line bends have thus farbeen illustrated, arcuate bends can also be achieved. One technique forproducing curved bend lines is shown in FIG. 33, namely, to layoutidentical strap-defining structures along a curved bend line so thevirtual fulcrums fall on the desired curved centerline.

[0300] Sheet 931 has been slit with identical slits 932 which arepositioned on opposite sides of curved bend lines 933 and folded into acorrugated panel. Slits 932 are shown as having a form similar to thesits of FIG. 6 with a central portion that is linear and diverging orcurving away end portions. Slits 932, however, are laid out bend lines.As radius of curvature of bend lines 933 decreases, the length of slits932 along bend lines 932 can be shortened to better approximate thecurve.

[0301] It should be noted that the corrugated sheet 931 has a hat-shapedcross section which is often found in roll formed corrugated panels.When used as a decking structure, this construction is not as desirableas the continuous panel of FIG. 20, because chord sheet portions 934only comprise about one-half the overall panel mass, but in otherapplications it has advantages and requires less material.

[0302] A second technique is to use non-identical strap-defining slitsto shape the bending straps to produce a smooth curved bend. The bentsheet will have curved surfaces on both sides of the bend line. Ifstepped slits are used, the longitudinally extending slit segments canbe shortened.

[0303] The distribution and width of bending straps may vary along thelength of a given bend-line for a variety of reasons including avariation in the trade-off between the local force required for bendingand the residual strength of the un-reinforced bend. For example,adjacent features that may be opportunistically formed at the same timeas the bending straps of the present invention may approach thebend-line so closely that the nearest bending straps are best formedwith less frequency near the approaching feature or with thinner strapsto maintain planarity of the bent material.

[0304] Finally, the bent structures of the present invention can beeasily unbent. This allows three-dimensional structures to bedisassembled or unfabricated for transport to another site or forrecycling of the sheet material. It has been found that the bent sheetmaterial can often be straightened out, or even subject to a bendreversal, and thereafter re-bent through 5 to 10 or more cycles. Thisallows bending or fabrication of a structure at one site and thenunbending, transportation and re-bending at a second site. The ease ofunbending also enables structures to be unbent and sent to a recyclingcenter for reuse of the sheet material and removed components.

[0305] For convenience in explanation and accurate definition in theappended claims, the terms “up” or “upper”, “down” or “lower”, “inside”and “outside” are used to describe features of the present inventionwith reference to the positions of such features as displayed in thefigures.

[0306] The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best utilize theinvention and various embodiments with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the claims appended hereto and theirequivalents.

In the claims:
 1. A sheet of material formed for bending along a bend line comprising: a sheet of material having a plurality of slits formed therethrough, the slits being positioned relative to a desired bend line and configured to produce bending of the sheet of material along the bend line with edge-to-face engagement of the sheet of material on opposite sides of the slits during substantially the entire bend of the sheet of material.
 2. The sheet of material as defined in claim 1 wherein, the sheet of material is formed with at least two elongated slits positioned proximate the bend line in longitudinally displaced positions relative to each other along the bend line, each slit having a slit end portion with a pair of adjacent slit end portions on opposite sides of the bend line defining a bending strap having a longitudinal strap axis extending across the bend line.
 3. The sheet of material as defined in claim 2 wherein, the slit end portions diverge away from the bend line.
 4. The sheet of material as defined in claim 3 wherein, the slit end portions are arcuate and curve away from the bend line.
 5. The sheet of material as defined in claim 2 wherein, the slits are positioned equidistant and on opposite sides of the bend line, and the slits are positioned in longitudinally overlapping relation to orient a longitudinal strap axis of the bending strap to extend at an oblique angle to the bend line.
 6. A sheet of material as defined in claim 1 wherein, the edge-to-face engagement occurs along substantially the full length of the slits during bending of the sheet of material.
 7. The sheet of material as defined in claim 1 wherein, the sheet of material is formed with at least two elongated slits positioned proximate and on opposite sides of the bend line in longitudinally staggered positions relative to each other along the bend line, and the slits each have substantially the same configuration, with the slit on one side of the bend line being inverted relative to the slit on the other side of the bend line.
 8. The sheet of material as defined in claim 7 wherein, the slits are symmetrical about a central transverse axis.
 9. The sheet of material as defined in claim 7 wherein the slits are asymmetrical about a central transverse axis.
 10. The sheet of material as defined in claim 1 wherein, the slits each have end portions and the longitudinally adjacent slit end portions define bending straps extending across the bend line that are symmetrical about a longitudinal strap axis.
 11. The sheet of material as defined in claim 1 wherein, the slits each have end portions and the longitudinally adjacent slit end portions define bending straps extending across the bend line that are asymmetrical about a central strap axis.
 12. The sheet of material as defined in claim 1 wherein, the slits each have substantially the same length along the bend line.
 13. The sheet of material as defined in claim 1 wherein, the slits have differing lengths along the bend line.
 14. The sheet of material as defined in claim 1 wherein, the slits are provided by a plurality of arcuate slits alternatively positioned on opposite sides of and longitudinally shifted along the bend line, the arcuate slits being convex in a direction facing the bend line and defining bending straps having strap axes extending obliquely across the bend line.
 15. The sheet of material as defined in claim 14 wherein, the sheet of material is formed with a plurality of pairs of longitudinally overlapping slits positioned laterally equidistant from the bend line to define the obliquely oriented strap axes.
 16. The sheet of material as defined in claim 15 wherein, the strap axes are oblique to the bend line in oppositely inclined directions.
 17. The sheet of material as defined in claim 1 wherein, the slits each have end portions, and the longitudinally adjacent slit end portions define bending straps having longitudinal strap axes extending obliquely across the bend line; and the strap axes are oblique to the bend line in the same direction to produce relative displacement along the bend line of portions of said sheet of material on opposite sides of the bend line upon bending of the sheet of material.
 18. The sheet of material as defined in claim 1 wherein, the slits have a kerf width which is sufficiently small so as to ensure edge-to-face interengagement of the sheet of material on opposite sides of the slits during bending.
 19. The sheet of material as defined in claim 1 wherein, the sheet of material is provided by a deformable sheet of one of: a metal, and a plastic.
 20. The sheet of material as defined in claim 18 wherein, the sheet of material is provided by a sheet which will only be elastically deformed during bending, and the slits are configured to orient the bending straps at an oblique angle which is sufficiently small to prevent plastic deformation of said sheet of material.
 21. The sheet of material as defined in claim 1 wherein, the slits are configured to cause an edge of the sheet of material along one side of the slits to engage and slide along a face of the sheet of material along the other side of the slits during bending.
 22. The sheet of material as defined in claim 2 wherein, the slits are formed with a stress reducing configuration at the ends of the slit end portions.
 23. The sheet of material as defined in claim 1 wherein, the plurality of slits includes a plurality of slits along and proximate the bend line configured to define at least one bending web between adjacent slit end portions, at least one slit being comprised of a first pair of longitudinally extending slit segments positioned proximate to and on opposite sides of and substantially parallel to the bend line, the longitudinally extending slit segments further having a pair of longitudinally proximate ends connected by a transversely extending slit segment.
 24. The sheet of material as defined in claim 1 wherein, the sheet of material is secured in a coiled condition.
 25. The sheet of material as defined in claim 2 wherein, the ratio of a jog distance between slits on opposite sides of the bend line to the thickness of the sheet of material is less than about 1.0, and the slits have a kerf less than about 0.3 times the thickness of the sheet of material.
 26. The sheet of material as defined in claim 2 wherein, the longitudinally adjacent ends of the slits define a bending strap extending across the bend line; and the bending strap is formed with a width dimension equal to between about 0.5 to about 4.0 times the thickness of the sheet of material.
 27. The sheet of material as defined in claim 26 wherein, the width dimension of the bending strap is between about 0.7 to about 2.5 times the thickness of the sheet of material.
 28. The sheet of material as defined in claim 1 wherein, the sheet of material has a plurality of slits positioned along a plurality of bend lines in positions producing edge-to-face engagement of the sheet material on opposite sides of each of the plurality of bend lines; and the sheet of material being bent along the plurality of bend lines to produce a three-dimensional structure.
 29. The sheet of material as defined in claim 28 wherein, the three-dimensional structure is a box beam.
 30. The sheet of material as defined in claim 28 wherein, the three-dimensional structure is a cross-braced box beam.
 31. The sheet of material as defined in claim 28 wherein, the three-dimensional structure is a chassis for electrical components.
 32. The sheet of material as defined in claim 28 wherein, the three-dimensional structure is a stud wall.
 33. The sheet of material as defined in claim 28 wherein, the three-dimensional structure is an origami form.
 34. The sheet of material as defined in claim 28 wherein, the three-dimensional structure is a corrugated panel.
 35. The sheet of material as defined in claim 28 wherein, the three-dimensional structure is a corrugated column.
 36. A sheet of material for bending along a desired bending line comprising: a sheet of material having a plurality of bending strap-defining structures formed therein, the strap-defining structures being positioned to define at least one bending strap in the sheet of material having a longitudinal strap axis oriented and positioned to extend across the bend line, and the strap defining structures being configured and positioned to produce bending of the sheet of material along the bend line.
 37. The sheet of material as defined in claim 36 wherein, the strap-defining structures are slits formed to extend through the sheet of material.
 38. The sheet of material as defined in claim 37 wherein, the slits have a kerf dimension and jog distance causing edge-to-face engagement of the sheet of material on opposite sides of the slits during bending of the sheet of material.
 39. The sheet of material as defined in claim 37 wherein, the slits are elongated arcuate slits.
 40. The sheet of material as defined in claim 39 wherein, the arcuate slits have convex sides facing the bend line.
 41. The sheet of material as defined in claim 36 wherein, the strap-defining structures are grooves formed to a depth not extending through the sheet of material.
 42. The sheet of material as defined in claim 41 wherein, the grooves are elongated arcuate grooves.
 43. The sheet of material as defined in claim 42 wherein, the arcuate grooves have convex sides facing the bend line.
 44. The sheet of material as defined in claim 41 wherein, the grooves are formed in the same side of the sheet of material.
 45. The sheet of material as defined in claim 36 wherein, the strap-defining structures define straps having a width dimension which increases in both directions along a longitudinal strap axis from about a midpoint of the length of the strap.
 46. A sheet of material formed for bending along a bend line comprising: a sheet of material having a plurality of slits formed therethrough in positions proximate and along the bend line, the slits each having opposite ends which diverge away from the bend line, and the slits being configured and positioned to produce bending of the sheet of material along the bend line.
 47. The sheet of material as defined in claim 36 wherein, the slits are alternatively positioned on opposite sides of the bend line, longitudinally adjacent slits have slit end portions defining a bending strap with a width dimension which increases as the bending strap extends away from the bend line.
 48. The sheet of material as defined in claim 36 wherein, the slits are each formed with a kerf dimension and a jog distance dimension relative to a thickness dimension of the sheet of material producing edge-to-face engagement of portions of the sheet of material on opposite sides of the slits during bending.
 49. A sheet of material formed for precision bending along a bend line comprising: a plastically and elastically deformable solid sheet of material having a plurality of elongated closed-ended slits therein positioned in end-to-end relation along and proximate to opposite sides of the bend line; and each slit having slit end portions diverging away from the bend line, with pairs of longitudinally adjacent end portions defining bending straps extending obliquely across the bend line.
 50. The sheet of material as defined in claim 49 wherein, the slits are positioned on alternating sides of the bend line and the slit end portions are arcuate and curve away from the bend line to define obliquely oriented straps skewed in alternating directions to the bend line.
 51. The sheet of material as defined in claim 49 wherein, the slits are arcuate and have convex side facing the bending line.
 52. The sheet of material as defined in claim 49 wherein, the bending strap is oriented for both twisting and bending during bending of the sheet of material.
 53. The sheet of material as defined in claim 49 wherein, a width dimension of the bending strap is greater than the thickness dimension of the sheet of material.
 54. The sheet of material as defined in claim 49 wherein, the bending strap has a thickness dimension which increases as the bending strap extends away from the bending line.
 55. The sheet of material as defined in claim 49 wherein, the plurality of slits define a plurality of bending straps extending across the bending line at oblique angles to the bending line.
 56. The sheet of material as defined in claim 55 wherein, alternative bending straps extend across the bending line in opposed skewed directions.
 57. The sheet of material as defined in claim 56 wherein, the sheet of material is a sheet of an isotropic material.
 58. The sheet of material as defined in claim 55 wherein, a plurality of the bending straps are skewed to extend across the bending line in the same direction.
 59. The sheet of material as defined in claim 58 wherein, the sheet of material is a non-isotropic material.
 60. The sheet of material as defined in claim 49 wherein, the slits are positioned substantially equidistance on the opposite sides of the bending line to produce bending of the bending strap about a virtual fulcrum substantially superimposed on the bending line, and wherein the transverse distance between slits across the bend line is not greater than about the thickness of the sheet of material.
 61. The sheet of material as defined in claim 49 wherein, the slits are formed to cooperate with the bending strap to displace the sheet of material on opposite sides of the slits out of engagement as the bending of the sheet of material is being completed.
 62. The sheet of material as defined in claim 49 wherein, the sheet of material is a sheet of an anodized metal.
 63. The sheet of material as defined in claim 49 wherein, each slit has arcuate end portions at opposite ends of the slit and the arcuate end portions are formed to curve in a direction away from the bend line.
 64. The sheet of material as defined in claim 63 wherein, the arcuate end portions extend to terminate at least the end of a zone of plastic deformation of the bending strap.
 65. The sheet of material as defined in claim 49 wherein, the sheet of material defining the slits has been outwardly compressed.
 66. The sheet of material as defined in claim 49 wherein, the slits are arcuate in shape and the tongue on the convex side of at least one slit is displaced laterally out of the plane of the sheet of material prior to bending of the sheet of material in order to bias the direction of bending of the sheet of material.
 67. The sheet of material as defined in claim 49 and, one of: a rub, dimple, contour, opening, flange, tab and groove formed in the sheet of material.
 68. The sheet of material as defined in claim 49 wherein, the slits are formed to extend through the sheet of material at an oblique angle to the plane of the sheet of material.
 69. The sheet of material as defined in claim 49 wherein, said sheet of material is a sheet of cast material having the slits cast therein.
 70. The sheet of material as defined in claim 49 wherein, the sheet of material defining the slits has been at least one of: deburred, electropolished, solvent etched, anodized, treated to reduce corrosion, and electroplated.
 71. The sheet of material as defined in claim 49, and an elastomeric layer bonded to the sheet of material across the bend line.
 72. The sheet of material as defined in claim 71 wherein, the elastomeric layer is decorated.
 73. The sheet of material as defined in claim 71 wherein, the elastomeric layer is reflective.
 74. The sheet of material as defined in claim 49 wherein, the sheet of material is a material having a thermally actuated shape memory.
 75. The sheet of material as defined in claim 49 wherein, said sheet of material carries an adhesive strip thereon.
 76. The sheet of material as defined in claim 49 and, a guard strip of material secured to the sheet of material over the bend line.
 77. The sheet of material as defined in claim 76 wherein, the guard strip is secured to a side of the sheet of material away from which the sheet of material is to be bent.
 78. The sheet of material as defined in claim 77 wherein, the guard strip is secured to a side of the sheet of material toward which the sheet of material is to be bent.
 79. The sheet of material as defined in claim 49 wherein, the sheet of material is formed for bending along a plurality of bend lines each having a plurality of slits therealong configured to produce edge-to-face engagement of the sheet of material on opposite sides of the slits during bending.
 80. The sheet of material as defined in claim 79 wherein, the plurality of bend lines are positioned and oriented to enable formation of a hollow closed structure upon bending of the sheet of material.
 81. The sheet of material as defined in claim 80 wherein, the plurality of bend lines are positioned and oriented to enable formation of a hollow curved beam upon bending of the sheet of material.
 82. The sheet of material as defined in claim 79 wherein, said plurality of bend lines are positioned and oriented to enable formation of a corrugated structure upon bending of the sheet of material.
 83. The sheet of material as defined in claim 80 wherein, the edges of the sheet of material are formed to mate with a curved surface.
 84. The sheet of material as defined in claim 83 wherein, the edges of the sheet of material are formed to mate with a cylindrical surface, and the hollow closed structure is a polygonal structure formed by a plurality of planar surfaces of said sheet of material between the plurality of bend lines.
 85. The sheet of material as defined in claim 79 wherein, the sheet of material is further formed with a plurality of attachment tabs along the plurality of bend lines.
 86. The sheet of material as defined in claim 85 wherein, the attachment tabs include fastener receiving openings therein.
 87. The sheet of material as defined in claim 85 wherein, the attachment tabs are formed to extend through attachment slots provided in a second sheet of material to secure the second sheet of material to the first named sheet of material.
 88. The sheet of material as defined in claim 79 wherein, the plurality of bend lines are substantially parallel to, and equally spaced from, each other, and the sheet of materials bent to have a zig-zag transverse cross section, and two substantially planar sheets of material secured to opposite sides of the sheet of material to provide a corrugated assembly of sheets.
 89. A hollow beam comprising: a first sheet of material formed for bending along a plurality of first sheet bend lines, the first sheet of material being formed with a plurality of slits therethrough positioned proximate each of the first sheet bend line, and the slits being configured to produce bending, and the first sheet of material being bent, along the first sheet bend lines; a second sheet of material formed for bending along a plurality of second sheet bend lines, the second sheet of material being formed with a plurality of slits therethrough positioned proximate each second sheet bend line, and the slits being configured to produce bending, and the second sheet of material being bent, along the second sheet bend tines; and the first sheet of material and the second sheet of material being secured together to form a hollow beam.
 90. The hollow beam as defined in claim 89 wherein, the slits in the first sheet of material and the slits in the second sheet of material are configured to produce edge-to-face engagement of the material on opposite sides of the slits during bending.
 91. The hollow beam as defined in claim 90 wherein, the slits in the first sheet of material and the slits in the second sheet of material are arcuate.
 92. The hollow beam as defined in claim 89 wherein, the first sheet of material and the second sheet of material are configured and secured together to form a cured hollow beam.
 93. The hollow beam as defined in claim 89 wherein, the first sheet of material is formed with slits positioned to extend along opposite sides of a pair of substantially parallel first sheet bend lines; the second sheet of material is formed with slits positioned to extend along opposite sides of a pair of substantially parallel second sheet bend lines.
 94. The hollow beam as defined in claim 93 wherein, the first sheet of material includes a plurality of notches extending inwardly from opposite edges of the first sheet of material to positions proximate the pair of first sheet bend lines; and the second sheet of material includes a plurality of notches extending inwardly from opposite edges of the second sheet of material to positions proximate the pair of second sheet bend lines.
 95. The hollow beam as defined in claim 94 wherein, the first sheet of material and the second sheet of material are each bent to have a U-shaped transverse cross section, and are secured together to form a four-sided hollow box beam.
 96. The hollow beam as defined in claim 95 wherein, the first sheet of material and the second sheet of material are bent to curve longitudinally along the bend lines, and are secured together to form a curved four-sided hollow box beam.
 97. The hollow beam as defined in claim 96 wherein, the notches in the first sheet of material and the second sheet of material are pie-shaped, and the first sheet of material and the second sheet of material are secured together by a plurality of fasteners.
 98. A cross-braced box beam comprising: a sheet of material formed for bending along a plurality of bend lines, the sheet of material being formed with a plurality of slits therethrough positioned proximate each of the bend lines, and the slits being configured to produce bending of the sheet into a box beam with at least two cross-bracing sheet portions positioned inside the beam, when bent to a three-dimensional form, the cross bracing sheet portions extending between alternating diametrically opposed corners of the box beam.
 99. A continuous corrugated deck comprising: a sheet of material formed for bending along a plurality of bend lines, the sheet of material being formed with a plurality of slits therethrough positioned proximate each of the bend lines, and the slits being configured to produce bending of the sheet into a corrugated deck having abutting chord sheet portions along both a top and a bottom side of the deck when bent into a three-dimensional form to provide continuous deck surfaces, and a plurality of connecting web sheet portions between the chord sheet portions.
 100. A chassis for support of components comprising: a sheet of material formed for bending along a plurality of bend lines, the sheet of material being formed with a plurality of slits therethrough positioned proximate each of the bend lines, and the slits being configured to produce a chassis; at least one component secured to the sheet; and the sheet being bent along the bend lines to at least partially enclose the sheet.
 101. A method of slitting a sheet of material for bending along a bend line comprising the step of: forming a plurality of slits through the sheet of material which are positioned relative to the bend line and configured to produce bending along the bend line with edge-to-face engagement of the material on opposite sides of the slits upon bending of the sheet of material.
 102. The method as defined in claim 101 wherein, during the forming step, forming the slits as arcuate slits alternating on opposite sides of the bend line with convex sides of the arcuate slits closest to the bend line.
 103. A method as defined in claim 101 wherein, during the forming step, each slit is formed with slit end portions diverging away from the bend line, with a pair of longitudinally adjacent slit end portions on opposite sides of the bend line defining a bending strap extending across the bend line, and during the forming step, forming the slits with a kerf width dimensioned and transverse jog distance between slits producing interengagement of the sheet of material on opposite sides of the slits during bending.
 104. The method of slitting a sheet of material for bending as defined in claim 103 wherein, the forming step is accomplished by forming the slits with slit end portions defining a bending strap extending obliquely across the bend line.
 105. The method as defined in claim 103, and the step of varying the cross sectional area of the bending strap by changing at least one of the jog distance between slits and the position of the slits along the bend line.
 106. The method of slitting a sheet of material for bending as defined in claim 101, and the step of: prior to the forming step, selecting a solid sheet of elastically and plastically deformable material for slitting.
 107. The method of slitting a sheet of material for bending as defined in claim 101 wherein, the forming step is accomplished by forming each of the slits in a position to longitudinally overlap along the bend line; and forming each slit with an arcuate end portion at each end of the slit to define an obliquely extending bending strap between the end portions of longitudinally adjacent slits.
 108. The method of slitting a sheet of material for bending as defined in claim 107 wherein, the forming step is accomplished by forming the slits to be laterally offset on opposite sides of the bend line with central slip portions substantially parallel to the bend line.
 109. The method of slitting a sheet of material for bending as defined in claim 108, the forming step is accomplished by forming the slits with a kerf producing sliding of edges on one side of the slit on faces on the other side of the slit during bending to position the edges in supporting relation to the faces of the sheet of material on opposite sides of the slits during bending.
 110. The method of slitting a sheet of material for bending as defined in claim 109, and the step of: after the forming step, bending the sheet of material about a virtual fulcrum aligned with the bend line to produce plastic and elastic deformation of the bending strap.
 111. The method of slitting a sheet of material for bending as defined in claim 101, wherein the forming step is accomplished by forming a plurality of slits as defined in claim 101 on opposite sides of the bend line along substantially the full length of the bend line.
 112. The method of slitting a sheet of material for bending as defined in claim 101, and the step of: after the forming step, bending the sheet of material about the bend line.
 113. The method as defined in claim 112 wherein, during the forming step, forming a plurality of slits on each of a plurality of intersecting bend lines; during the bending step, bending the sheet of material along at least two bend lines to produce a structure having three mutually intersecting and abutting planar sheet panels; and the step of: securing the three mutually intersecting panels in abutting relation for mutual support.
 114. The method as defined in claim 112, and the step of: after the bending step, filling the bent sheet of material at the slits by one of a welding, brazing, soldering, potting and adhesive filling step.
 115. The method of slitting a sheet of material for bending as defined in claim 101 wherein, the forming step is accomplished at a first location, and the steps of: after the forming step, transporting the sheet of material from the first location to a second location remote of the first location; and after the transporting step, bending the sheet of material along the bend line at the second location.
 116. The method of slitting a sheet of material for bending as defined in claim 115 wherein, the transporting step is accomplished by transporting the sheet of material in one of: (a) a flat condition; (b) a coiled condition; and (c) a partially formed condition.
 117. The method of slitting a sheet of material for bending as defined in claim 115 wherein, after the forming step and prior to the transporting step, rolling the sheet of material into a coil, performing the transporting step while the sheet of material is coiled, and the step of: uncoiling the sheet of material at another location prior to performing the bending step.
 118. The method of slitting a sheet of material for bending as defined in claim 117, and the step of: during the uncoiling step, performing the bending step.
 119. The method as defined in claim 118 wherein, the transportation step is accomplished by transporting the coiled sheet of material from a first location on the surface of the surface of the earth to a second location in outer space.
 120. The method as defined in claim 119 wherein, the bending step is accomplished by bending the sheet of material along a plurality of bend lines to produce a structure having three mutually intersecting planes; and the step of securing the structure against unbending.
 121. A method of forming a sheet of material for bending along a bend line comprising the step of: forming a plurality of bending strap-defining structures in the sheet of material which are positioned relative to the bend line to define at least one bending strap in the sheet of material having a longitudinal strap axis oriented to extend across the bend line, the strap-defining structures being configured and positioned with edge-to-face engagement of the material to produce bending of the sheet of material along the bend line.
 122. The method as defined in claim 121 wherein, the forming step is accomplished by forming the strap-defining structures as slits extending through the sheet of material.
 123. The method as defined in claim 122 wherein, the forming step is accomplished by forming the slits to have a kerf dimension and jog distance causing edge-to-face engagement of the sheet of material on opposite sides of the slits during bending of the sheet of material.
 124. The method as defined in claim 121 wherein, the forming step is accomplished by forming the slits as elongated arcuate slits.
 125. The method as defined in claim 124 wherein, the forming step is accomplished by forming the arcuate slits to have convex sides facing the bend line.
 126. The method as defined in claim 121 wherein, the forming step is accomplished by forming the strap-defining structures as grooves formed to a depth not extending through the sheet of material.
 127. The method as defined in claim 126 wherein, the forming step is accomplished by forming the grooves as elongated arcuate grooves.
 128. The method as defined in claim 127 wherein, the forming step is accomplished by forming the arcuate grooves to have convex sides facing the bend line.
 129. The method as defined in claim 126 wherein, the forming step is accomplished by forming the grooves in the same side of the sheet of material.
 130. The method as defined in claim 121 wherein, the forming step is accomplished by forming the strap-defining structures to define straps having a width dimension which increases in both directions along a longitudinal strap axis from about a midpoint of the length of the strap.
 131. The method as defined in claim 121 wherein, the forming step is accomplished by forming the strap-defining structures as arcuate slits defining tongues on a concave side of the arcuate slits displaced out of the plane of the sheet of material before bending.
 132. The method as defined in claim 122 wherein, during the forming step, forming the slits as arcuate slits alternating on opposite sides of the bend line with convex sides of the arcuate slits facing the bend line.
 133. A method as defined in claim 121 wherein, during the forming step, each slit is formed with slit end portions diverging away from the bend line, with a pair of longitudinally adjacent slit end portions on opposite sides of the bend line defining the bending strap extending across the bend line, and during the forming step, forming the slits with a kerf width dimensioned producing interengagement of the sheet of material on opposite sides of the slits during bending.
 134. A method of slitting a sheet of material for bending along a bend line comprising the steps of: selecting a solid sheet of material for slitting; and forming a plurality of slits along a desired bend line with alternate slits along the bend line being positioned on alternating sides of the bend line and during the forming step, forming each slit with a central portion substantially parallel to and offset laterally from the bend line and with arcuate slit end portions on each end of the slit curving away from the bend line so that adjacent pairs of arcuate slits define bending straps extending obliquely across the bend line with increasing strap width dimensions on both sides of a minimum width dimension.
 135. The method as defined in claim 134 wherein, the forming step is accomplished using a laser cutting apparatus to cut slits having a kerf width dimensioned to produce interengagement of the sheet of material on opposite sides of the slits during bending.
 136. The method in claim 134 wherein, the forming step is accomplished using a water jet cutting apparatus to cut slits having a kerf width dimensioned to produce interengagement of the sheet of material on opposite sides of the slits during bending.
 137. The method as defined in claim 134, and the step of: after the forming step, bending the sheet of material along the bend line.
 138. The method as defined in claim 137 wherein, the forming step is accomplished by forming the slits with a kerf width dimension and a transverse jog distance between slits producing sliding interengagement of an edge of the sheet of material on one side of the slit with a face of the sheet of material on the other side of the sheet of material; and the bending step is accomplished by bending the sheet of material about a virtual fulcrum substantially aligned with the bend line so that sliding interengagement of edges and faces of the sheet of material produces plastic and elastic deformation of the bending straps.
 139. The method as defined in claim 138 wherein, the forming step is accomplished by forming the slits along a plurality of intersecting bend lines; and the bending step is accomplished by bending the sheet of material into a three-dimensional structure having three intersecting planar areas extending into abutting relation; and the step of securing the three intersecting planar areas together to form a stable structure.
 140. The method as defined in claim 138, and the step of: after the bending step, filling the slits with a material producing a sealed joint at the bend line.
 141. The method of claim 140 wherein, the filling step is accomplished by one of: (a) welding; (b) brazing; (c) soldering; (d) potting; and (e) adhesive filling.
 142. The method of claim 138, and the step of: after the bending step, unbending the sheet of material.
 143. The method of claim 134 wherein, the forming step is accomplished by providing slits defining bending straps oriented relative to the bend line to oppositely extending oblique angles.
 144. The method of claim 143 wherein, the forming step is accomplished by providing bending straps having longituding strap axes oriented relative to the bend line at angles of about 45° and about 135° at opposite ends of a slit.
 145. A method as defined in claim 134 wherein, the forming step is accomplished by selecting a width dimension for the bending straps producing a desired amount of force required to bend the sheet of material.
 146. A method as set forth in claim 134 wherein, the forming step is accomplished by selecting a minimum width dimension for the bending straps which is greater than the thickness of the sheet of material being bent.
 147. A method as set forth in claim 134 wherein, the forming step is accomplished by selecting a minimum width dimension for the bending straps which is less than the thickness of the sheet of material being bent.
 148. A method as set forth in claim 134 wherein, the forming step is accomplished by selecting a minimum width dimension for the bending straps which is in the range of about 0.5 to about 4 times the thickness of the sheet of material being bent.
 149. A method as set forth in claim 148 wherein, the selecting step is accomplished by selecting a minimum width of the bending straps to be between 0.7 to 2.5 times the thickness of the material being bent.
 150. A method as set forth in claim 134 wherein, the forming step is accomplished by configuring the bending straps to be oriented obliquely to the bending line in oppositely skewed directions.
 151. A method as set forth in claim 150 wherein, the forming step is accomplished by configuring the bending straps to diverge from proximate a midpoint of the lengths of the bending straps.
 152. The method as defined in claim 134 wherein, the steps of selecting the sheet of material and forming a plurality of slits are accomplished to produce only elastic deformation of the sheet of material during bending.
 153. The method as defined in claim 134 wherein, the forming step is accomplished in a manner producing sliding edge-to-face engagement of the sheet of material on opposite sides of the slits, the sliding engagement progressing from a longitudinal center of the slits to the slit ends as the bending straps are twisted and bent.
 154. The method as defined in claim 134 wherein, during the forming step, the minimum width of the bending straps, the distance of each slit from the bend line, and the width of each slit are selected to produce a desired strength of the bend for the composition and thickness of said sheet of material and the forces to which the bend is to be subjected during use.
 155. The method of claim 134 wherein, during the forming step, the distance of each slit to the bend line is less than the thickness of the sheet of material.
 156. The method of claim 134 wherein, during the step of forming the slits, the slits are formed to have a geometry which tends to reduce residual stress in the sheet material at the point where the slits are terminated.
 157. The method as defined in claim 137 wherein, the forming step is accomplished by forming the slits along a plurality of bend lines arranged to produce a cross-braced box beam upon bending; and during the bending step, bending the sheet of material into a cross-braced box beam.
 158. The method as defined in claim 137 wherein, the forming step is accomplished by forming the slits along a plurality of bend lines arranged to produce a continuous corrugated deck upon bending; and during the bending step, bending the sheet of material into a continuous corrugated deck.
 159. The method as defined in claim 137 wherein, the forming step is accomplished by forming the slits along a plurality of bend lines arranged to produce a component support chassis upon bending; and during the bending step, bending the sheet of material into a component support chassis.
 160. The method as defined in claim 137 wherein, the forming step is accomplished by forming the slits along a plurality of bend lines arranged to produce a stud wall upon bending; and during the bending step, bending the sheet of material into a stud wall.
 161. The method as defined in claim 137 wherein, the forming step is accomplished by forming the slits along a plurality of bend lines arranged to produce a ladder upon bending; and during the bending step, bending the sheet of material into a ladder.
 162. A method of forming a three dimensional structure comprising the steps of: forming a plurality of bend-facilitating structures in a sheet of material, the plurality of bend-facilitating structures being configured and positioned relative to a plurality of bend lines to produce bending of the sheet of material along the bend lines; bending the sheet of material along a first bend line; bending the sheet of material along at least one additional bend line until two portions of the sheet of material are abutting; and coupling together two abutting portions of the sheet of material to produce a rigid load bearing three-dimensional structure capable of supporting three-dimensional loading.
 163. The method as defined in claim 162 wherein, during said forming step, forming said bend facilitating structures as slits having a kerf producing edge-to-face contact during the bending step.
 164. A method of designing a three-dimensional structure comprising the steps of: laying out in a CAD system a plurality of bend-facilitating structures to be placed in a sheet of material, the plurality of bend-facilitating structures being configured and positioned relative to a plurality of bend lines to allow bending of the sheet of material along the bend lines; and forming said bend-facilitating structures in said sheet of material identically to the way said structures are laid out on said CAD system, such that when said sheet is bent along at least two bend lines two portions of said sheet will be abutting and said abutting portions may be coupled together to produce a rigid load bearing three-dimensional structure capable of supporting three-dimensional loading.
 165. A method of designing a product comprising the steps of: laying out the design of the product in two dimensions, wherein said product is to be made from a folded sheet of solid material; and designing the configuration of and positioning for at least two slits to be formed in the sheet of solid material, with each slit to be located in a laterally offset position on opposite sides of a desired bend line and to be longitudinally displaced relative to the other slit along the bend line, the slits to be configured to produce interengagement of solid edges of said sheet of solid material on opposite sides of the slits during bending of the sheet of solid material.
 166. A method of making a product comprising the steps of: laying out the design of the product in two dimensions on a sheet of material; designing the configuration of at least two elongated slits to be formed in the sheet of material with each slit being laterally offset on opposite sides of a desired bend line and being longitudinally displaced relative to the other slit along the bend line, the slits being configured to produce interengagement of solid edges of the sheet of material on opposite sides of the slits during bending of the sheet of material; forming the slits in the sheet of material as designed and positioned; and bending the sheet of material along the bend line to form the product.
 167. The method as defined in claim 166, and the additional step of: prior to the bending step, shipping the formed sheet of material in a flat state for bending of the sheet of material at a remote location.
 168. The method as defined in claim 166, and the additional step of: bending the sheet of material at the remote location about a virtual fulcrum aligned with the bend line to produce deformation of the sheet of material along the bend line and interengagement of solid edges of the sheet of material.
 169. A method of folding a sheet of isotropic material along a fold line comprising the steps of: forming a plurality of arcs on the sheet of material, each of the arcs defining a plurality of connected zones between ends of the arcs, the arcs being symmetrically and longitudinally spaced on opposite sides of the fold line, the connected zones forming straps extending obliquely across the fold line; and folding the sheet of material along the fold line.
 170. The method as defined in claim 169 wherein, the forming step is accomplished by forming the arcs to define straps aligned in opposite directions along the fold line so that the planes of the sheet of material on opposite sides of the fold line do not shift when the sheet of material is folded along the fold line.
 171. The method as defined in claim 169 wherein, during the forming step, forming the arcs to produce connected zones extending obliquely across the fold line in the same direction; and during the bending step, allowing the sheet of material on opposite sides of the fold line to shift longitudinally along the fold line.
 172. A sheet of material formed for bending along a bend line comprising: a sheet of material having at least two bending straps formed to extend across the bend line, the straps having a minimum width dimension proximate the bend line and increasing in width dimension as the straps extend away from both sides of the minimum width dimension, and the straps being positioned relative to a desired bend line and being configured to produce plastic deformation of the straps at the bend line upon bending of the sheet of material along the bend line.
 173. A method of bending a sheet of non-compressible material along a bend line comprising the steps of: forming a plurality of connected arcs on said sheet, each of said arcs creating a connected zone and a disconnected zone in said sheet, wherein said arcs are symmetrically and longitudinally spaced along said bend line, wherein said connected zones form straps across said bend line, and wherein said disconnected zones have biased tabs that remain somewhat deflected in one of a downward or upward bias from said sheet upon bending, said tabs assisting in correctly initiating edge to face engagement of said disconnected zones throughout the length of said bend line upon bending; and bending said sheet along said bend line such that a plane of said sheet shifts relative to said another plane of said sheet along said bend line.
 174. A method as set forth in claim 173 wherein said deflected bias of said tabs prevents said tabs from sliding under or over the opposite face of said sheet thereby preserving the integrity of said bending process.
 175. A method as set forth in claim 174 wherein said bending occurs in the opposite direction from said deflected biased tabs.
 176. A method of preparing a sheet of material that is only elastically deformable for bending along a bend line comprising the step of: forming a plurality of connected large radius arcs on said sheet, each of said arcs creating a connected zone and a disconnected zone in said sheet, wherein said arcs are symmetrically and longitudinally spaced along said bend line and wherein said connected zones form straps across said bend line and wherein said bend line terminates at a free surface comprising one of an exterior edge and an interior edge.
 177. The method of claim 176 wherein said free surface is an exterior edge wherein said bend terminates in one of: a. an exterior edge at or near a perpendicular edge with respect to said bend line; b. an interruption of a disconnected zone across said bend line near a bend edge with a strap between said interruption and said bend edge with said bend perpendicular or nearly perpendicular to said bend line; c. a significantly non-perpendicular angle to said bend line where the angle of a bend line is used as one edge of a terminating strap; d. an exterior bend edge of a strap is near a radius corner, where said last arc is rotated so as to form said strap at said bend edge; and e. a terminal arc rotated to the other side of said bend line so as to coincide with the curvature of a radius corner and thus form a final strap of said bend.
 178. A method of precisely bending a non-compressible sheet of material comprising the step of: bending said sheet in a manner such that upon bending said sheet to a given degree of sharpness in the bend, the microstructure of said material undergoes very little change in comparison to bending said sheet of material to substantially the same degree of sharpness using conventional bending techniques.
 179. A method of precisely bending a non-compressible sheet of material comprising the step of: bending said sheet in a manner such that upon bending said sheet to a given angle of sharpness in the bend, the microstructure of said material undergoes very little change in comparison to bending said sheet of material to substantially the same angle of sharpness using conventional bending techniques.
 180. A method of designing a part made of non-compressible sheet of material for bending along a bend line, comprising the step of: laying out at least two bending straps in spaced apart and oblique relation along a proposed bend line in said sheet of material such that said sheet of material will be plastically deformed by both twisting and bending upon bending of said sheet of material, whereby the bending is made easier and the material is strengthened along the bend line.
 181. A method of making a machine comprising the steps of: making at least one component of the machine, where that component is made from an elastically and plastically deformable solid sheet of material by a method comprising the steps of: a. forming two elongated slits through the sheet of material with each slit being laterally offset on opposite sides of a desired bend line and being longitudinally displaced relative to the other slit along said bend line, said slits having a kerf width dimension producing interengagement of solid edges of said sheet of material on opposite sides of said slits during bending; and b. bending said sheet of material about a virtual fulcrum aligned with said bend line to produce plastic and elastic deformation of said sheet of material along said bend line and interengagement of said solid edges; and assembling all components necessary to finish making the machine.
 182. A method of designing a product comprising the steps of: laying out the design of the product in two dimensions, wherein said product is made of an elastically and plastically deformable solid sheet of material; and designing at least two elongated slits in the sheet of material with each slit being laterally offset on opposite sides of a desired bend line and being longitudinally displaced relative to the other slit along said bend line, said slits having a kerf width dimensioned producing interengagement of solid edges of said sheet of material on opposite sides of said slits during bending of said sheet of material.
 183. A method of designing an enclosure comprising the steps of: 1) laying out the design of said enclosure in two dimensions, wherein said enclosure is made of an elastically and plastically deformable solid sheet of material; 2) forming at least two elongated slits in the sheet of material with each slit being laterally offset on opposite sides of a desired bend line and being longitudinally displaced relative to the other slit along said bend line, said slits having a kerf width and jog distance dimensioned producing interengagement of solid edges of said sheet of material on opposite sides of said slits during bending; and 3) repeating step 2 as many times as necessary for the number of bends contained in said enclosure.
 184. A method of making an enclosure from an elastically and plastically deformable solid sheet of material comprising the steps of: 1) forming at least two elongated slits through the sheet of material with each slit being laterally offset on opposite sides of a desired bend line and being longitudinally displaced relative to the other slit along said bend line, said slits having a kerf width and jog distance dimension producing interengagement of solid edges of said sheet of material on opposite sides of said slits during bending; 2) repeating step 1) as many times as necessary for the number of bends contained in said enclosure; and 3) bending said sheet of material about each virtual fulcrum aligned with each of said bend lines to produce plastic and elastic deformation of said sheet of material along each of said bend lines and interengagement of said solid edges.
 185. A method as in claim 5 wherein an additional step comprises: sealing the enclosure so that it permanently conforms to the finished shape of said enclosure.
 186. A method of making a part made of a non-compressible sheet of material for bending along a bend line, comprising the step of: creating at least two bending straps in spaced apart and oblique relation along a proposed bend line in said sheet of material such that said sheet of material will be plastically deformed by both twisting and bending upon bending of said sheet of material, whereby the bending is made easier and the material is strengthened along the bend line.
 187. A sheet of material formed for bending along a bend line comprising: a sheet material which is elastically deformable having a plurality of slits each comprised of a plurality of longitudinally connected arcs on the sheet, each slit being configured and positioned relative to a desired fold line to produce a connected zone and a disconnected zone in the sheet wherein the slits are symmetrically and longitudinally spaced along the fold line and wherein the connected zones have a relatively small angle from the fold line.
 188. A sheet of material formed for bending along a bend line comprising: a sheet of material having a slit formed therethrough and positioned proximate a desired bend line, and a bending strap at each end of the slit, the bending strap being configured to produce bending of the sheet of material along the bend line with edge-to-face engagement of the sheet of material on opposite sides of the slit during substantially the entire bend of the sheet of material.
 189. The sheet of material as defined in claim 188 wherein, the slit has slit end portions diverging away from the bend line and defining one side of each bending strap.
 190. The sheet of material as defined in claim 189 wherein, the slit end portions are arcuate and curve away from the bend line.
 191. The sheet of material as defined in claim 188 wherein, the bending straps extend obliquely across the bend line.
 192. The sheet of material as defined in claim 191 wherein, the bending straps are skewed in opposed directions converging toward each other on a side of the bend line opposite the slit.
 193. The sheet of material as defined in claim 188 wherein, a side of one bending strap is defined by an edge of the sheet of material.
 194. The sheet of material as defined in claim 193 wherein, the slit has arcuate end portion at each end and one end portion and the edge of the sheet of material define an obliquely extending bending strap.
 195. The sheet of material as defined in claim 188 wherein, the sheet of material has been bent along the bend line.
 196. A method of bending a sheet of material formed for bending along a bend line comprising the step of: forming a slit through a sheet of material, said slit being positioned relative to a desired bend line and being configured to produce bending of the sheet of material along the bend line with edge-to-face engagement of the sheet of material on opposite sides of the slit during substantially the entire bend of the sheet of material.
 197. The method of claim 196 wherein, the forming step is accomplished by forming said slit having end portions, each of said end portions defining one side of a bending strap extending obliquely across the bend line.
 198. The method of claim 197 wherein, said slit is arcuate with a convex side, said convex side of said slit being closest to the bend line.
 199. The method of claim 196 wherein, the forming step is accomplished by forming the slit proximate an edge of the sheet of material so that the edge and an arcuate end of the sheet of material define a bending strap.
 200. A method of designing a sheet of material for bending along a bend line comprising the step of: laying out a slit on a sheet of material, said slit being positioned relative to a desired bend line and configured to define with a structure on the sheet, a bending strap at each end of the slit oriented to produce edge-to-face engagement of the sheet of material on opposite sides of a slit upon bending of the sheet of material during substantially the entire bend of the sheet of material.
 201. The method of claim 200 wherein, the laying out step is accomplished by forming said slit having end portions, each of said end portions defining a bending strap that extends obliquely across the bend line in oppositely skewed directions that converge on a far side of the bend line from the slit.
 202. The method of claim 201 wherein, the forming step is accomplished by forming the slit as an arcuate slit with a convex side being positioned closest to the bend line.
 203. A method of forming a sheet of material for bending along a bend line comprising the step of: forming a plurality of bending strap-defining structures in the sheet of material which are positioned relative to the bend line to define at two bending straps in the sheet of material at opposite ends of a slit through the sheet of material, the bending straps each having a longitudinal strap axis oriented to extend across the bend line, the strap-defining structures being configured and positioned relative to the slit to produce edge-to-face engagement of the material on opposite sides of the slit during bending of the sheet of material.
 204. A method of slitting a sheet of material for bending along a bend line comprising the steps of: selecting a solid sheet of material for slitting; and forming a slit along a desired bend line with a central portion substantially parallel to and offset laterally from the bend line and with arcuate slit end portions on each end of said slit curving away from the bend line so that said end portions of said arcuate slit define at least part of bending straps extending obliquely across the bend line with increasing strap width dimensions on both sides of a minimum width dimension of the straps.
 205. A method of designing a product comprising the steps of: laying out the design of the product in two dimensions, wherein said product is to be made from a folded sheet of solid material; and designing the configuration of and positioning a slit to be formed in the sheet of solid material, said slit to be located in a laterally offset position along a desired bend line, said slit to be configured to produce interengagement of solid edges of said sheet of solid material on opposite sides of said slit during bending of the sheet of solid material.
 206. A method of designing a non-compressible sheet of material to be bent along a bend line comprising the step of: laying out a slit and a bending strap on each end of the slit on the sheet in a manner such that upon bending the sheet to a given angle of sharpness in the bend, the microstructure of the sheet of material undergoes very little change in comparison to bending the sheet of material to substantially the same angle of sharpness using conventional bending techniques.
 207. The method as defined in claim 206 and the step of: forming the sheet with the slit and bending straps; and bending the sheet along the bend line.
 208. A method of designing a product comprising the steps of: laying out the design of the product in two dimensions, wherein said product is to be made from a folded sheet of solid material; and designing the configuration of and positioning a slit to be formed in the sheet of solid material, said slit to be located in a laterally offset position along a desired bend line, said slit to be configured to produce interengagement of solid edges of said sheet of solid material on opposite sides of said slit during bending of the sheet of solid material. 